Djourou played the 90 minutes in their Carling Cup win over Tottenham.
Wenger told arsenal.com: "The competition is very hard for him but I have a lot of understanding for Johan because he was out for a year and you do not come straight back [to your best] in a month.
"You need four centre backs for a season. I believe personally that we have four good centre backs, not only good but very good centre backs.
"Johan was a midfielder and that's why he likes to come out and play with the ball but he is as well tall, strong in the air and quick. He has all the assets to become a very good centre back."