Wenger said he was worried about an injury that will keep Walcott out of Saturday's match at Newcastle United and makes him a doubt for England's upcoming friendly against Slovakia and World Cup qualifier against Ukraine.
"We are surprised and worried," Wenger said on Arsenal's website. "He was in very good form coming back and that is very bad news for us and for England.
"For the rest of the season might be too long, but he's out of tomorrow's squad and he could be out of the England squad."
The extent of the 20-year-old winger's injury is not yet clear but Wenger told reporters it could be a cartilage problem.
"We have to see how he responds today and I hope it's not really serious," Wenger said.
Walcott missed 22 matches with a shoulder injury before returning to the side as a late substitute against Burnley in their FA Cup fifth round match on March 8.
The good news for Arsenal is that striker Eduardo has been passed fit for the Newcastle game.
Eduardo returned to the team recently after a long injury lay-off before missing the last two matches with a groin problem.
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