It is another blow for the Gunners, who lost captain Cesc Fabregas to a broken leg during the Champions League quarter-final first leg against Barcelona on Wednesday night.
And although Wenger expects Andrey Arshavin to be back in his side within three weeks, the Russian striker has himself admitted that he may not be ready to return before the end of the campaign either.
End of the road: William Gallas holds his head in his hands as he stretchered off during the Champions League clash against Barcelona on Wednesday, while Andrey Arshavin was also forced out of the action (below)
Gallas, who is out of contract at the end of the current campaign, had been somewhat rushed back from missing eight games with a calf problem.
However, after being unable to finish the Barcelona game, Wenger confirmed the French centre-back was unlikely to recover in time to play again this season.
Wenger said: 'Gallas is longer than three weeks, I would say five weeks. It was a gamble which did not pay off and was a mistake, yes.
'He could be back maybe quicker, but I just give myself five weeks because three weeks is a minimum and we will have to be a bit more cautious with him.
'So when we go to the Champions League final, he still has a chance to play.'
The Arsenal manager expects Arshavin to be available again by the visit of Manchester City on April 24.
However, the Russian international feared the injury is more serious than was first diagnosed.
'I think I have torn it (calf muscle),' he was quoted as saying by the Sport-Express newspaper.
'If that's true, then I'll be out for a long time, at best after three weeks but at worst I won't play at all this season.'
Defender Gael Clichy (back) and midfielder Denilson (groin) have both been passed fit for tomorrow's home game against Wolves.
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