The Germany international has not scored in his last eight Premier League matches and failed to record an assist since December.
However, Wenger has dismissed suggestions the former Real Madrid man was any worse than his teammates at Anfield, and says the 25-year-old is still finding his feet in English football.
The Frenchman told reporters: "He works very hard to adapt to the Premier League. For me he's an exceptional player.
"He was like everybody else on Saturday [in the 5-1 defeat to Liverpool]. He works very hard in training to improve."
Arsenal will need to re-find its defensive solidity to contain a star-studded Manchester United attack on Wednesday night, which contains former north London frontman Robin van Persie, and Wenger is confident the collapse at Anfield was just a blip.
"Van Persie is a great player," the Gunners boss continued. "It's down to how well we defend against him tomorrow.
"We've been very stable until now defensively. We have to consider how well we have done until now."
Wenger was then asked about recent rumors that Van Persie might be open to a return to the Emirates at the end of the season.
"I don't think it’s the best time to talk about that," the 64-year-old stated.
Meanwhile, Wenger confirmed that Arsenal has no new injury problems to contend with after Saturday's defeat at Anfield, while Yaya Sanogo is back to full fitness and available to face United.