Walcott is struggling with a shoulder injury while Gallas is doubtful with a hamstring problem and a decision on both players will be made in the next 24 hours.
"Mikael has a broken nose with an open wound on the side," said Wenger.
"Basically he should be capable of playing. But in the next 48 hours I will have to decide what we do.
"You cannot rule him out and I feel he can play. But I have to decide whether I go for the gamble or not."
"Almunia was back in training today so he will be available," said Wenger.
"As for Sagna, there was a gamble on him that I did not want to take last night.
"We could not take it today in training either. He still needed to be out of impact work.
"I think he should be OK for Saturday but there is still a slight concern."