"I believe it is difficult for a player when he doesn't play regularly to be absolutely exceptional," Wenger told the club's website.
"I don't think he had a bad game but I think he suffered a little bit from the fact we were not as sharp as we might have been.
"Your confidence is not at the top as well when you don't play for one month. You need to play regularly.
"He will come back. He works hard in training and has a good attitude so we just have to keep him tight."