So Arsenal let a two-goal slip as Walcott and Giroud efforts are cancelled out by Huntelaar and Farfan. There will be a regret for Arsenal but they probably would have taken a point before kick-off. Olympiakos beat Montpellier which means all is still to play for in the group. Arsenal's trip to Olympiakos on the final group game could yet be a knock-out meeting. Stay with us for all the post-match reaction.
90 + 4
FULL-TIME: SCHALKE 2 ARSENAL 2
90 + 4
What a chance for Walcott. He gets behind the Arsenal defence and manages to get a shot away but it hits the legs of Unnerstall.
90 + 4
Schalke make their final change. Barnetta is on in place of Holtby.
90 + 3
The ball is not sticking for up top for Arsenal but Schalke are not exactly causing too many scares. Fuchs' cross goes behind.
90 + 2
Coquelin has the chance to get his head up close to the Schalke box and he looks for a pass to Giroud. The striker cannot make anything of it and takes a bit of a whack in the back from a defender.
90 + 1
ADDED TIME: There will be a minimum of four minutes added time before the final whistle.
Arsenal make a double change. Santos and Coquelin come on in place of Cazorla and Podolski.
More good work from Mannone as he vitally punches clear a cross just as Huntelaar's eyes were lighting up.
Arsenal go on a rare move forward and Walcott wants a free-kick on the edge of the box. It looked like he could have had a case but play is waved on and Schalke win a throw-in deep in Arsenal territory.
Schalke are seeing all of the ball in the final minutes. Arsenal cannot get a kick at the moment. But they are keeping Schalke in deep areas.
The Schlake fans let Vermaelen know what they think as he hobbles off the pitch having received treatment.
Possibly running down the clock but Vermaelen goes down after a slide tackle and is receiving treatment.
Huntelaar cannot quiet get over the top of a cross as he heads over the crossbar. He was offside anyway bit that is a warning as the final whistle approaches.
This is very unlike Wenger this season not to have made any substitutions. Will tired legs pay the price in the closing minutes?
Podolski tries to latch onto a bouncing ball inside the penalty area but the highly-rated Papadopoulos gets his body in the way to prevent the Germany player from meeting the ball.
Mannone has probably been Arsenal's man of the match this evening. He has made several very important saves.
Jones forces another good save from Mannone after cutting in from the right with a low show to the near post.
The game has become a little scrappy. Both sides now look as if they are focusing on not losing the game rather than going gung-ho for the winner.
Wilshere makes a tired challenge on Jones close to the touchline. The Arsenal youngster looks out on his feet at the moment.
Jones is the next player to be booked after raising his arms in an aerial challenge with Vermaelen.
Howedes has been pushed to right-back since Hoger's exit and he sends a cross high over the Arsenal crossbar.
It remains to be seen if Wenger will yet decide to make any changes. He does not really have a great deal of trusted options on the bench.
After conceding the equaliser, Arsenal have cleared their heads and they are looking like they could yet find a winner.
Walcott hits the post after collecting a pass from Koscielny. But it would not have counted as a flag went up correctly and belatedly for offside.
Arsenal remain on the front foot with a passage of pressure. However, Walcott's cross is far too deep and goes out for a Schalke throw-in on the far side.
Corner to Arsenal on the right. But Cazorla's delivery is headed clear at the near post.
Wilshere takes another whack in midfield and does not look happy as he gets to his feet. He looks very tired having just returned from injury.
Now Mertesacker slips and that allows Holtby to break into the penalty area. He tries to cross a pass to Huntelaar but cannot find his team-mate. Big let off for Arsenal.
From a cross from the left, Farfan is left free at the back post. He has time and space to take a touch before firing a shot from close range. It was probably sneaking in at the back post but a deflection off Vermaelen ensures in flies into the back of the net. Arsenal have let a two-goal lead slip.
GOAL FARFAN (2-2)!!!
Bad news for Schalke as they have to take off substitute Hoger, who has not recovered from that injury. Papadopoulos comes on.
Replays show that Holtby effort took a little nick off Koscielny on its way towards goal. That makes it an even better save from Mannone.
Hoger, walking a little delicately, is back on after receiving treatment on the touchline. Holtby is offer too much room around 25 yards from goal and Mannone does well to palm away his swerving effort.
Hoger hobbles off the pitch after receiving some treatment. Schalke return the ball to Arsenal and deep into the Premier League team's territory.
Podolski goes in the book for kicking the ball away in frustration. He was annoyed, because Arsenal were on the attack inside the penalty area but referee Rizzoli decided to halt play for an injury to Hoger. It was not a head injury.
From the corner, Hoger slides in to hit a combination of Arteta and post for the ball to deflect behind for another corner. The second set-piece is headed wide.
Walcott defends well when tracking back on Afellay to give away a corner - Schalke's ninth of the game.
Poor ball from Wilshere otherwise Walcott might have been in. Unnerstall can instead come and get the ball.
Tempers are beginning to rise. Podolski and Howedes go head-to-head. The Schalke captain was not happy with his Germany team-mate for a challenge.
Arsenal have a rare chance to move up the field in the second half. Sagna prods a pass to Walcott, who thinks he is through on goal but is pulled back for offside.
Replays show the ball definitely hit Mertesacker on the arm. But it is ball to arm at short-range. Referee Rizzoli cannot really give that.
Wenger's team again only half-clear the corner. Holtby crosses low from the right and there is a mass scramble in the Arsenal box. The ball appears to strike the arm of Mertesacker and Schalke are screaming for a penalty. Play is waved on.
Arsenal just about clear the corner. But Fuchs keeps play alive with another cross. Huntelaar nods the ball down for Jones, whose shot deflects for another corner.
Wilshere loses the ball in midfield and Schalke move forward. Arteta slides in at the near post to stab Afellay's cross out for a corner.
It will be a surprise if there are not more goals in this game. Both teams look very open at the back.
Fine save from Mannone to preserve Arsenal's lead. Huntelaar's movement sees him get behind the Arsenal defence and go one-on-one with Mannone. The goalkeeper stays on his feet until the last minute and manages to deflect the shot for a corner, which Arsenal clear.
Arsenal need to be careful not to take too many risks at the back. Koscielny almost over does it on the edge of his own box and just manages to get out of trouble.
Schalke are playing a very high line at the start of the second half. They could be there for the taking on the counter-attack with Walcott's pace.
Break in play for Wilshere to get back to his feet after Holtby accidentally trod on his heel off the ball. Holtby is very apologetic.
Great chance for Giroud. Cazorla and Podolski double up on Hoger and the latter can cross. He finds Giroud at the back post but the forward volleys into the ground and over the crossbar.
From the re-start, Farfan attacks down the right against Vermaelen but, not for the first time tonight, the Schalke wide-man runs the ball out of play.
WE'RE BACK: Schalke get the second half under way. Neither team have made any substitutions at the break.
Greg says: "Arsenal urgently need to buy a new left-back. Gibbs is way too injury prone and Santos...well don't even get me started on Santos."
Huntelaar's goal is the last kick of the half and that will put nerves into Arsenal's team at the interval. They had taken the lead through Walcott and Giroud but always looked like conceding. There look like there will be more goals in this game. Do Arsenal need to make any changes in tactics or personnel at the break? Let me have your thoughts at firstname.lastname@example.org or via Twitter @SkySportsPeteF.
45 + 2
HALF-TIME: SCHALKE 1 ARSENAL 2
That is a huge setback for Arsenal on the stroke of half-time but they never looked comfortable. Cazorla slipped and lost the ball in his own half and, from an excellent Holtby pass, Huntelaar fires a low, first-time, left-foot shot past Mannone and inside the far post from inside the penalty area. Clinical, trademark finish from the Dutchman.
45 + 2
GOAL HUNTELAAR (1-2)!!!
45 + 1
Schalke's fans are getting frustrated. There are shrill whistles around the stadium as the team play back to Unnerstall.
ADDED TIME: There will be a minimum of two minutes added time before half-time.
Cazorla sends in another dangerous free-kick. His inswinging right-footer has to be punched clear by Unnerstall within his six-yard box.
Podolski is giving substitute Hoger, who is a midfielder by trade but is having to play at left-back, problems. The Arsenal man wins a free-kick close to the left corner flag
From the resulting free-kick, Cazorla flights a wonderful delivery to the edge of the six-yard box and Giroud meets the ball. The striker wastes the chance and heads straight at Unnerstall.
Fuchs is the next play to go in the book after a studs-up, late challenge on Walcott. That was nasty and a correct yellow card.
It will be hugely important for Arsenal to get to half-time with their two-goal lead in tack. But Vermaelen is beginning to struggle with Farfan. The Arsenal captain slips and Farfan shoots just wide from 25 yards.
More good defending from Arsenal. Vermaelen heads a cross clear and Wilshere is very cunning to get his body in between the ball and Fuchs to win a free-kick on the edge of his own box and relieve some pressure.
Schalke are building up another period of pressure. Farfan is allowed room to cross but is unable to find a team-mate from the right byline.
Arsenal have done well to keep Huntelaar quiet. But the Dutchman is always in the right place when a cross comes into the box and he has only been inches away from a few deliveries.
Good defending from Koscielny, who holds off Farfan and allows the ball to roll out for a goal-kick.
Arsenal do look like they have more goals in them. Schalke are having to take a few risks at the back and Podolski was free at the back post in an attack but the ball did not make its way that far.
After making the compulsory trip off the field following treatment, Giroud is back on and seems to be okay.
There is another break in play for treatment to Giroud, who clutched the back of his right leg after landing following a jump for a header.
The goals have clearly rocked Schalke. They were breaking at great speed in the first 15 minutes but are now stuttering.
Schalke win another corner. Jones gets his head to the ball but cannot direct it towards goal and only flicks it on and clear. Arsenal will be grateful.
Podolski has been guilty of losing possession in midfield on a couple of occasions. He will need to cut that out.
Schalke turnover possession in midfield by tackling Podolski and break forward. Sagna does well to stop the ball from reaching Huntelaar.
Wenger celebrated that second goal by punching the air. He understandably looked very happy. Schalke will be wondering what has happened after such a strong start.
Great work from Podolski down the left as he holds off Hoger, who had only just come on for the injured Uchida, before whipping in a cross. With the Schalke defence flat-footed, Giroud attacks the ball and dives to head in from six yards.
GOAL GIROUD (0-2)!!!
Hoger comes on in place of Uchida.
Wilshere clears another cross on the edge of his own box and finds Cazorla. As the Spaniard breaks forward, he is ruthlessly tripped by Matip, who is booked.
Play is back under way and Schalke have corner from the right. Farfan's delivery is poor and Wilshere can touch it away on the edge of the box. Uchida's follow-up is well wide.
There is a break in play for Uchida to receive treatment. It looks like he has hurt his right thigh.
Cazorla goes in the book for an intentional handball when diving to stop the ball as it rolled past him in midfield.
Arsenal now look full of confidence. Podolski charges down the left and whips in a cross. The cross is just over the head of Walcott at the back post.
Schalke really shot themselves in the foot. They had started very well but conceded through unforced errors.
A catastrophic back-header from Neustadter is pounced on by Giroud and he breaks clear of the Schalke defence for a one-on-one with Unnerstall. Giroud makes a real mess of the chance and clatters into the Schalke goalkeeper and Howedes. But Walcott has followed-up and is able to roll the ball into the open goal. Against the run of play but a great start for Arsenal and Walcott makes his point.
GOAL WALCOTT (0-1)!!!
Arsenal's second corner goes deeper. Giroud manages to keep play alive before the ball falls towards Podolski inside the box. The ball will not quite drop for the German and Unnerstall can collect.
Better from Arsenal. Sagna plays the ball to Wilshere, who goes on a quick run and wins a corner. The first corner goes short to Wilshere in the box and Neustadter has to make the tackle to give away another corner.
Uchida has clearly been told to attack Vermaelen. Again, the Schalke right-back gets to the byline and Arsenal are relieved to see him run the ball out for a goal-kick.
Wenger will be annoyed his team are not managing to put any passes together in Schalke's half. As a consequence, Sagna decides to resort to a long ball to Giroud, which is easily cleared.
Arsenal are maintaining their zonal marking system and it is almost exposed as Howedes gets a run on the ball and heads it before Giroud at the corner. His effort goes just over the crossbar.
Walcott might be trying to do a bit too much when he has the ball. He again tries to take on more than one Schalke player and is tackled. Schalke move up the field and win a corner on the right.
Arsenal are struggling to keep the ball. Wilshere, Arteta and Cazorla have not really influenced the game in the opening 11 minutes.
Schalke are breaking at speed at every chance. Afellay bursts forward after Podolski gave the ball away and forces a save from Mannone with a shot from inside the penalty area
There was a little bit of afters from Fuchs on Walcott and the Schalke defender earns a ticking off from referee Rizzoli.
Excellent tracking back from Walcott as he darts in to tackle Fuchs and then win his side a throw-in.
Schalke's corner is headed clear at the near post. But it is not overly convincing and Schalke keep the ball in the centre of midfield. The home team are dominating the centre of midfield in the very early minutes.
Schalke counter-attack and left-back Fuchs is in an advanced position. His shot from 20 yards deflects for a corner.
Wilshere has a bit of room in midfield and finds Walcott, who takes on three Schalke defenders on the edge of the box before being tackled.
Poor from Podolski when Arsenal are on the attack as he attempts to thread a pass through the eye of a needle to Giroud rather than keep the ball. Schalke regain possession.
Again Uchida goes forward down the right. This time, Podolski is back to give Vermaelen a bit of cover.
Much has been made of Arsenal's failure to press opponents in Europe when they have the ball. The Premier League club are happy to let Schalke's defenders have the ball until they approach the halfway line.
In the opening 60 seconds, Schalke target Vermaelen at left-back. Uchida gets forward from right-back and manages to cross from the byline but he cannot find a team-mate.
KICK-OFF: Arsenal, in their changed kit of yellow, get the game going.
The Champions League anthem is over, the pre-match handshakes are complete and there is a very loud atmosphere in the stadium.
Schalke captain Howedes and Arsenal skipper Vermaelen lead their team-mates out of the tunnel in Gelsenkirchen. Kick-off is just minutes away.
Do not forget to stay with us after the final whistle. We will have all the post-match reaction, including a full report on the game, manager and player quotes, interactive player ratings and analysis.
I am looking forward to watching Wilshere. This is a night when Arsenal need leaders and, even at just 20 years of age, he is his side's main man on the field despite not being captain. He will also be keen to make up for his sending off against United.
A few people are saying the same thing about Vermaelen. The Arsenal skipper was not at his best against Manchester United and he could be playing left-back tonight, which would put him up against the dangerous Farfan.
If you fancy a flutter, Sky Bet have a range of markets available tonight. Arsenal are 16/5 to get a much-needed win against Schalke, who are 8/1 for a repeat of their 2-0 win at the Emirates. Huntelaar scored and was dangerous for Stevens' men two weeks ago and he is part of our double chance price boost. The former Ajax man is 11/1 to score first with Schalke to win 1-0 or 2-0, while Gunners striker Walcott receives a recall to the starting XI and is 66/1 to score first in a 1-0 Arsenal win.
Helawi says: "I'm so relieved that Santos has been dropped. He is simply useless!! I also can't understand why this season they seem to be so deflated. This is not the first time they've lost two games in a row."
Richard Allen says: "Glad to see Walcott starting tonight. I think he could be instrumental tonight as has to prove he is worth a pay rise and can see Arsenal wining 1-2. Cazorla and Walcott the scorers."
Jordan Harris says: "I'm a lifelong Gooner but I can't see us getting anything tonight. I hope Walcott shows his worth to confirm his contract."
If you joined us late, shame on you. But here is a round-up of the team news. Wenger has dropped under-fire Santos. The Brazil left-back has been under the spotlight since swapping shirts with Robin van Persie at half-time of Saturday's 2-1 defeat at Manchester United and is replaced in the starting line-up by Koscielny. Walcott overcomes illness and comes in for the injured Aaron Ramsey in Arsenal's only other change, while Schalke name the same side who lost 3-2 at Hoffenheim despite manager Stevens hinting at changes before the game.
Gabriel says: "If Arsenal come away with a draw, in our current form, I'd be pleased. Dropping Santos is the right move, because as much as I love him, he is the most clueless defender in the world. If we want to come out with a win, we need to put the past behind us."
Why are Arsenal in this position? What has gone wrong this season? They have reached the knockout stages of the Champions League for the past 12 successive campaigns.
Referee: Mauro Tonolini (ITA). Assistant referees: Renato Faverani (ITA) Andrea Stefani (ITA). Additional assistant referees: Antonio Damato (ITA) Paolo Valeri (ITA). Fourth official: Mauro Tonolini (ITA).
Can Arsenal overcome that loss to Schalke at the Emirates, where Huntelaar and Afellay scored? What do you make of the team news? Are you pleased to see Santos dropped to the bench? Do not forget you can get in touch at email@example.com or via Twitter @SkySportsPeteF.
It really does look a tough night for Arsenal amid their current problems - domestic defeats by Norwich City and United - and with Schalke sitting second in the Bundesliga. But the German club did surrender and eight-game unbeaten run in all competitions in Saturday's loss at Hoffenheim.
Stevens has resisted the temptation to reinstate Hildebrand in goal in place of Unnerstall while the highly-rated Papadopoulos is also only on the bench.
After losing to Schalke at Emirates Stadium, surrendering a 45-game unbeaten home record against foreign teams, this is an important night for Arsene Wenger's Arsenal as the Frenchman returns from a three-match touchline ban. But Schalke will be no pushovers and a win, combined with Olympiakos slipping up against Montpellier would put Huub Stevens' side in the knockout stages.
So Walcott has returned to Arsenal's line-up on a night when they really have to win to avoid leaving their Champions League hopes hanging by a thread. Santos has been dropped to the bench after his performance against Manchester United. What do you think?
Arsenal team: Mannone, Sagna, Koscielny, Mertesacker, Vermaelen, Wilshere, Arteta, Walcott, Cazorla, Podolski, Giroud. Subs: Shea, Santos, Djourou, Coquelin, Arshavin, Jenkinson, Chamakh
Schalke team: Unnerstall, Howedes, Uchida, Fuchs, Matip, Holtby, Jones, Neustadter, Afellay, Farfan, Huntelaar. Subs: Hildebrand, Marica, Hoger, Papadopoulos, Moritz, Draxler, Sead Kolasinac
You can get in touch throughout the evening with your predictions, opinions and, possibly, rants on the game. Drop me a line at firstname.lastname@example.org or via Twitter @SkySportsPeteF and I will publish a selection of the best comments.
Hello and welcome to our live and interactive coverage of Arsenal's crucial UEFA Champions League meeting with Schalke in Gelsenkirchen. Stay with us for all the team news.