The 20-year-old has not featured at all for the Gunners this season after picking up a heel injury during pre-season.
A series of setbacks during the campaign mean that the England international will miss the Euro 2012 championships in Poland and Ukraine this summer.
However, Wenger has now said that he is not entirely certain whether the creative midfielder will be back in time for the start of next season.
"He makes slow progress and at the moment is still in a rehab centre," said the Frenchman. "We take time, we are patient with him. He makes progress, but slow progress.
"When we start pre-season on July 9, if he can join in, then we have won the battle. But that is not guaranteed."
Wenger also criticised Pearce's insistence that no manager has the power to veto the call from him this summer.
"You cannot say [Pearce's] statement was completely helpful. If you say: 'you can go to Olympics' and he doesn't make it, what do you give him after? Let's take our time and not set any specific targets. The most important thing for him is to focus on day to day work and see if he can get better."
Wilshere last played competitively in England's 2-2 draw with Switzerland in June.