Wenger added: "I don't know if Gallas has been perturbed by his departure from Arsenal.
"I knew he wouldn't be at 100 per cent for this tournament. The question for the manager is to know if he should have called up Gallas while knowing he's not 100 per cent.
"He's played 35 minutes in four months before here.
"It's not enough to get into a competition like this. When you don't know where you are physically, a player is always fragile.
"William is a boy with great will, he's a winner. But he wants to do well so badly that sometimes he puts a lot of pressure on himself."