The Gunners moved to push through a deadline-day deal with Malaga, believed to be for £8.5million, after England defender Kieran Gibbs hobbled out of Wednesday's Premier League draw against Liverpool with a thigh problem.
Gibbs could now be out for up to eight weeks, missing the Champions League tie against Bayern Munich for which Monreal will be cup-tied.
While happy to have secured the services of such an experienced player, who could make his debut at home to Stoke on Saturday, Wenger accepts Arsenal can only tighten up at the back with improved team displays.
"What we want him to do is to take part in our collective game and not expect anything especially individually because our game is based on team play and he has been chosen because he can integrate that," said Wenger, who watched his team fall 2-0 against Liverpool before mounting a comeback.
"He has the characteristics to play our game because he is very mobile, has a good left foot and is very good in combination play, which is of course vital in our style of play.
"We just have to keep going with the quality and get the nervous side out of our game."
Monreal has been on Wenger's radar for some time, although not one of the many names linked with a January switch to Emirates Stadium.
The Gunners boss felt it was important to bring in experienced cover, with out-of-form Brazilian Andre Santos the only other recognised left-back.
"Our scouts have followed his progress for a while and of course we had a blow with the Gibbs injury, which is a bit longer than expected," Wenger said.
"We expected two to three weeks, now it will be four to six, so we were in a position where we had to make a quick decision. That explains our buy."
Wenger continued: "I believe we need two left-backs. You cannot play every single game with the same player. We had two before, we have two again now.
"If Gibbs is out for four to six weeks, from six it can easily go to eight [before he is competitive again] and that means two months in a very decisive period, so it is vital to have another left back."
Wenger has yet to decide whether Monreal will go straight into the side to face Stoke on Saturday, but revealed midfielder Mikel Arteta could be back from his lay-off with a calf injury. Centre-back Thomas Vermaelen aggravated an ankle problem against Liverpool and will be assessed today.
Arsenal were linked with a host of players during the January transfer window, including Barcelona forward David Villa and West Ham's Senegal midfielder Mohamed Diame.
Wenger admitted there was some frustration he was not able to get at least one more body in.
"We were close to one more signature, yes," the Gunners boss said.
"It was not a money problem, it was more a desire from other clubs to keep their players."
Despite not being able to further bolster the group, Wenger has every confidence they can finally deliver consistency over the final four months of what has been a stop-start campaign.
"I believe that we have top quality in our squad and that is what we want to show until the end of the season," he said.
"The game against Liverpool shows the quality we have, but we also have some aspects in our game that we need to improve.
"How active we will be in the market in the summer will be decided how well we do now until the end of the season."
Arsenal have a strong record against Stoke at Emirates Stadium.
Wenger, though, is not expecting an easy ride against Tony Pulis' men, who the Gunners boss believes have again raised their game.
"When you play Stoke, you always expect a fierce resistance, a very committed game and unfortunately, you are never disappointed. You always get what you expect," he said.
"I believe they have improved their technical quality as well, with players like Steven Nzonzi and Charlie Adam, therefore they have more variety in their game than they had in previous years."