It's completely heartbreaking for the Hoops, who were one minute away from a monumental result. Barca get the victory they wanted but you can't help feel for brave Celtic, who gave everything for their fans and their club tonight. Thanks for your company and the Camp Nou and I'll see you all soon.
90+4 FULL TIME. Barcelona 2 Celtic 1.
It's late heartbreak for Celtic, as Adriano's curling ball to the far post clips the outstretched foot of Alba who nods it past Forster.
90+4 GOAL FOR BARCELONA - ALBA!
Two more minutes of injury time to be played!
Villa hits the post! The drama is absolutely overwhelming here as the striker's effort flies through Wilson's legs but cannons straight back off the woodwork.
Hooper is presented with a great chance to break from the corner but Mascherano steps in after a loose touch from the striker.
Alba grabs a stroke of luck to play a one-two off Wilson but Wanyama does enough to concede the corner.
Celtic are working so hard to ensure Barca don't grab a late winner, and as they work an opening, Tello can only stab an effort wide from 20 yards.
Barca probe but Celtic remain organised and resilient, forcing a frustrated Xavi into a wild shot from range which ends up with the home fans.
Forster is on hand after some divine Barca movement. Messi and Iniesta combine again but the latter's ball lands too close to the Celtic keeper who gobbles up the ball.
Celtic are momentarily down to 10 men as Wanyama receives treatment, a dangerous position against arguably the world's greatest ever side.
Wanyama remains in the wars as he goes down with cramp, an example of just how much effort the Hoops have put into this game so far.
Tello cuts in from the right, but Song can only head over from close range as Wanyama takes a crunching clash from the midfielder in the process.
Wilson makes another outstanding tackle on the edge of the area to deny Messi. It would be truly heartbreaking for the SPL giants if Celtic concede a late goal here.
80 Sanchez's night comes to an end as Villa comes on in his place.
80 Yellow card for Adriano after a clumsy trip on Commons.
Sanchez's battle with Ludwig ends in a Barca throw as the hosts begin to throw everything but the kitchen sink at Celtic now.
77 Celtic make a change in kind as Mulgrew is replaced by Kayal.
76 Barca make a change with Pedro replaced in favour of Tello.
Forster again is in the form of his life. Iniesta finds Messi in space but his header is somehow parried behind goal by the Celtic keeper!
Commons aims for Hooper over the top of Mascherano but the centre-back is fortunate the ball lands on his chest and he can comfortably claim.
Forrest looks to run at Barca again but Iniesta does excellently. As Barca probe into Celtic's six-yard box, Sanchez is denied by the masterful Forster at the near post.
Commons releases Forrest quickly, but his driven ball into the six-yard box takes a touch of Bartra and ends up being a comfortable knock-down for Song to Valdes.
70 Brilliant work from Forrest agai, who surges forward before taking a lunge from Mascherano. Yellow card for the Barca man and a free-kick for Celtic,
Celtic are getting extremely sloppy in possession, and as Barca break, an essential tackle from Wilson nudges Messi out wide when he was seemingly poised to unleash a shot from the edge of the box.
What a save from Forster! An exquisite move from the hosts saw Pedro pick out Messi in the six-yard box with the Celtic keeper making a wonderful point blank save from the Argentine.
A lovely passage of play sees Celtic's defence lose concentration as Iniesta finds space, before driving a shot straight at Forster. It will be interesting to see how long Celtic's brave defenders can go before completely tiring here.
Messi lets rip from 25 yards but it's an effort met by another impressive show of handling from Forster.
At this point, Celtic really do look as likely to scoring as Barca. They are defending valiantly but they just can't find that necessary quality in the final third.
Commons breaks away from Alba and with Hooper sprinting in at the far post, his ball is just too weak and is easily picked up on by Mascherano in the end.
63 Brown is taken off by Celtic and Commons comes on - the captain's armband handed to Ledley.
Wilson throws his foot out to cut out Messi, and as Celtic look to counter, their only form of attack at the moment, through Mulgrew, Barca's defence narrows and he's intercepted.
Lustig sticks his body in the way of Iniesta's pass to Alba, with Celtic continuing to defend doggedly against the waves of Barca attack.
Wanyama breaks away as Celtic look to charge forward. He delays a pass to Hooper for too long though and Mascherano steps in with a precise tackle.
Forrest looks to take the ball away for Celtic, but Brown is blocked off by Barca bodies and he's easily intercepted by Bartra.
Pedro is back defending, and doing a marvellous job of it as he cuts out a pass from Hooper and draws a foul from Mulgrew.
The corner is again played short, and Adriano's drive from range, while packing a punch, is straight down the throat of Forster.
Lustig provides cover to head clear Messi's ball, but Pedro does brilliantly to keep it in play, earning a corner off Wilson as his reward.
Sublime passing from Iniesta and Sanchez results in the former reaching the byline. His touch carries the ball a tad too far though and Wilson covers as the ball rolls out of play.
Another great chance for Celtic. A corner from Mulgrew clips the head of Ambrose, with Bartra's pressure enough to force the ball wide.
Messi's vision is out of the world as he displays a tremendous first touch from Xavi's pass before attemptng to chip Forster, his effort landing on the roof of the net.
Lennon is fuming on the touchline after Wanyama's run was blocked off by Alba. No free-kick is given and play continues.
Mulgrew has a pop from the free-kick but it cannons off the wall. Izaguirre shoots from the rebound but ends up sailing the ball some way over the bar.
Brilliant work from Forrest, who wins a free-kick after a mazy run which lures Alba into making the challenge 20 yards from goal.
Forrest does well initially to track back and intercept from Sanchez. He ends up playing back to Alba though as the hosts regain control of the ball.
Iniesta evades the tackle of Wanyama and Barca push down the left. Sanchez aims for goal but Messi takes a touch which ends up allowing Ambrose to clear.
Sanchez can't find Iniesta, and ends up conceding a free-kick as he vies with Ludwig for control of the ball.
Barcelona kick off the second half.
Nathan Ofoluwa writes: "Sorry Celtic fans but Barcelona will win this easy, Pedro and Sanchez to score or if in doubt Messi."
Celtic come agonisingly close to reaching half time with the lead, but Iniesta's goal has cancelled out Samaras' opener after a wonderful first 45 minutes. Send your second half predictions to email@example.com or @JWoodfield365
HALF TIME. Barcelona 1 Celtic 1.
Messi comes close to giving Barca the lead, but his eventual shot after an exchange with Sanchez results in a shot heading wide.
Barca equalise in the most glorious of fashion. Messi to Iniesta, to Xavi, back to Iniesta, and a wonderful finish amongst a host of Celtic bodies. It's 1-1 and you'd back Barca to come out storming after the break.
45 GOAL FOR BARCELONA - INIESTA!
44 Samaras is indeed forced off as Forrest comes on in his place.
Lustig heads away a chip from Messi, before brilliant work from Hooper earns Celtic a very timely free-kick.
Celtic threaten from a set piece again, as Ledley's delivery results in an attempted over-head kick from Ambrose which is eventually booted away by Mascherano.
Samaras resisted the stretcher but he is severely hobbling as he awaits treatment on the sidelines.
Samaras is down, and he has issued a gesture which appears his game may be over.
Ambrose shows good anticipation to steal the ball away from Messi, with Barca seeming to struggle as they continue to carve out chances using their Plan A technique of scoring.
Messi again comes close. His second free-kick lands on the roof of the net once more but this time Forster flies across goal for the fear of it creeping underneath the crossbar.
Wanyama stays strong to dispossess Iniesta but he can't take Celtic forward. Messi then draws a free-kick 30 yards out as Brown slides in.
Sanchez picks out Messi and the inspirational front man goes for goal with an outstretched foot than nearly caught Forster unawares. In the end it's a Hoops free-kick.
Hooper holds up the ball momentarily, and Celtic enjoy a rare spell of possession which is cheered passionately by their fans in attendance.
Celtic continue to make sure that final pass is always cut out in their penalty box, but as soon as they win the ball back, Samaras is cut off by Song.
Adriano goes for the near post from range, but Forster shows good handling to claim and then keep the ball after an initial spillage.
Messi's ball is cut out by Ludwig but Iniesta's sublime skill nearly results in a chance for Sanchez - before the Celtic bodies close in and prevent a shot.
Excellent work from Barca as Xavi, Pedro and Messi link up, with Messi's final ball to Xavi cut out by the oncoming Forster.
Great chance for Barca. Bartra is in the thick of it again as he meanders into the six-yard box and clips a delivery from Iniesta, his header skimming marginally wide of goal.
Pedro takes a terrible touch as he lines up to shoot, with Ambrose using that moment to make another exceptional tackle.
Alba looks to get involved down the left, but as soon as he ventures to meet Iniesta's header, the offside flag is raised.
Adriano holds the ball as Brown goes sliding, but when he does pull the trigger a terrific tackle from Wilson denies the ball hitting the target.
Song plays a careless pass through the centre and Celtic look to break. Hooper picks it up on the right but his cut back to Hooper is cut out by Mascherano.
Barca win a free-kick roughly 25 yards, cue Messi. His strike from 25 yards curls but it narrowly skips the roof of the net.
Ambrose again does brilliantly to intercept a deflection from Iniesta's pass, cutting off Sanchez to clear the ball to touch.
Adriano heads to the byline as Barca look to retaliate, driving the ball across ball but tremendous defending from Ambrose sees the ball cleared.
Incredible scenes! A Celtic free-kick proves fruitful as Samaras' header clips Mascherano who ends up sending the ball past his own goalkeeper. It's 1-0 to Celtic!
18 GOAL FOR CELTIC - SAMARAS!
Forster makes the first save of the match as Barca play the corner short - Messi finding Iniesta who chips in with Bartra's header punched away at the near post.
Celtic only regain possession for four passes until Wilson's clearance lands at the feet of Xavi. Barca attack again as Adriano's powerful effort is nodded behind for a corner by Ludwig.
Alba and Pedro link up down the left, winning a corner which is again played short. Messi is found by Iniesta, the forward playing the ball into the six-yard box where it is cleared by Wilson.
Celtic look to capitalise on a trip from Iniesta, but the excellence that is Xavi tracks back and forces the error from Samaras to regain possession.
Celtic's work-rate is already being tested to the limit, as they chase and hussle Barca, before Iniesta is tripped by Brown.
Xavi and Iniesta link up before the former tries to find Sanches between Celtic's centre-backs. He slightly draws his pass to the left though and Forster is able to claim.
Samaras shows too much enthusiasm chasing Ludwig's long ball and ends up conceding a foul on the grateful Bartra.
Aidan Pidgeon writes: "Tonight is a massive night tonight for Celtic, it could be the making of Samaras, Wanyama and Hooper all 3 are important tonight. Let's roll back 2004 when we beat Barcelona and play like that night again at the Nou Camp, that was a great night one I'll never forget."
Messi looks to cause havoc on the edge of the box, before playing in Alba. The left back whips the ball across the face of goal but good marking from Wilson prevents Sanchez from making contact.
Adriano just catches Izaguirre as the Celtic man looked to play the ball down the line and as a result a free-kick is awarded.
Mascherano plays an uncharactertiscally poor ball long to Sanchez, the forward given no chance as it rolls out for a Celtic goal kick.
Alba earns Barca a corner, which is played short back to Alba. Messi and Song then look for a one-two on the edge of the box but Song's ball is hacked away by Ambrose.
Barca probe for an opening with Celtic forced to chase shadows. The hosts have already begun their tiki taka play in excellent fashion this evening.
Alba draws a foul from Brown as Barca look incredibly menacing early on. From the free-kick the hosts lose control down the right and Ambrose clears.
Mascharano gives the ball away with a poor pass, but Hooper can't sort his feet out and Song gathers. Moments later, Barca come agonisingly close to taking the lead as Iniesta plays in Sanchez and the forward shoots wide from 15 yards.
We're underway as Celtic kick off.
Examining that team news further, skipper Scott Brown, Georgios Samaras, Mikael Lustig and Emilio Izaguirre return to the Celtic side. Defender Kelvin Wilson shrugs off a calf injury picked up in Saturday's SPL win over St Mirren, while Kris Commons and James Forrest recover from respective hamstring and groin injuries which kept them out of the trip to Paisley to take their place on the bench. Barca coach Tito Vilanova has several regular defenders out injured which leads to him giving 21-year-old Marc Bartra his first game of the season alongside midfielder Javier Mascherano in central defence. Argentina star Lionel Messi goes into the match on the back of a hat-trick in Saturday's 5-4 win over Deportivo La Coruna.
The referee for tonight is Gianluca Rocchi (Italy).
Celtic: Forster, Lustig, Wilson, Ambrose, Izaguirre, Samaras, Brown, Wanyama, Ledley, Mulgrew, Hooper. Subs: Zaluska, Matthews, Miku, Commons, Rogne, Kayal, Forrest.
Barcelona: Valdes, Adriano, Bartra, Mascherano, Jordi Alba, Xavi, Song, Iniesta, Sanchez, Messi, Pedro. Subs: Pinto, Fabregas, Villa, Jonathan, Montoya, Sergi Roberto, Tello.
Here are the teams....
Cian Hughes writes in: "I honestly i support both teams and think this is the most important game of the Champions League so far! It is really difficult to decide who I want to win, so i think I will go for a draw at 2-2, Messi and Xavi for Barcelona & Hooper and Wanyama for Celtic."
Can Celtic's defence stop Lionel Messi at the Nou Camp? Sky Bet's customers don't think they can and the Argentine is 6/4 to net first against Neil Lennon's side and an incredible 1/5 to score anytime. Messi to score first and Barca to win 5-0 has been well backed at 18/1. Celtic are buoyed by their win at Spartak Moscow in their last match but are 22/1 to spring an upset tonight with the four-time champions 12/1 on to secure a third straight Champions League win.
Good evening everyone and welcome to the Camp Nou for the Champions League qualifying Group G clash between Barcelona and Celtic. From the outlook, this game has the potential to be one of the more memorable of this season's campaign, especially after Celtic's positive start and the fact that both teams scored five goals in their most recent league games. Some may be predicting a mauling tonight but a Celtic win would be the biggest upset of the competition so far. If you'd like to drop me a line tonight you can e-mail firstname.lastname@example.org or tweet @JWoodfield365
Kick-off is 1945 BST.