"He had a hamstring problem, came back after nearly out for four weeks, now he has a groin problem," said Wenger.
"At the moment, he is more prone to muscular problems but we have not found the real reason.
"You could see when he's fit he's a very important player to us, but when he comes back from injury it takes him two or three games to get back to his best, so it is vital for him and for us that we sort out his muscular problem.
"I do not think it is linked with the training regime. It is true it is intense but because he is a very genuine player on the pitch he plays always a bit like an engine that turns at 6,000rpm. He always plays to the maximum."