The Polish goalkeeper is mentally affected from all the action he has seen this season and will be replaced by Vito Mannone as the Gunners try to reverse their 3-1 loss in the Round of 16 first leg in North London three weeks ago.
"He has played many games since the start of the season and recently I felt that mentally it affected him, that is why I have decided to rest him," Wenger told reporters.
"[He has been affected] by the number of games he has played. It is his second season only in the Premier League and he has played many games.
"I am always confident before the game that the guy who plays is ready. The players who start our games have no excuse of not being fit or ready. If I decide to play them it is because they are ready."