Manager Arsene Wenger confirmed to reporters on Thursday that the knee ligament damage Gallas suffered during his side's 1-1 draw at Villarreal meant he would play no further part in Arsenal's assault on the Champions League and FA Cup trophies.
Gallas was injured when he collided with Villarreal striker Giuseppe Rossi shortly before half-time.
Arsenal will also be without goalkeeper Manuel Almunia for three weeks due to an ankle injury which he suffered in Tuesday's match in a collision with Rossi while full-back Gael Clichy will miss two weeks with a back injury.
Almunia's absence means that second-choice goalkeeper Lukasz Fabianski, who replaced Almunia after 27 minutes in Spain, will have an extended run in the team for the first time this season.
Robin van Persie and Eduardo, who both missed Tuesday's match, are struggling to be fit for Saturday's Premier League match against Wigan Athletic and will undergo fitness tests before the game.
ARSENAL FANS! Check FourFourTwo.com’s ever-expanding interviews archive for more stuff to read:
Web Exclusives Patrick Vieira, Cesc Fabregas
Q&A Theo Walcott, Cesc Fabregas
One on One Arsene Wenger, Thierry Henry, Ian Wright
Boy's A Bit Special Theo Walcott, Armand Traore
Perfect XI Ian Wright
What Happened Next? Gus Caesar, Peter Marinello
And Another Thing Being a Big Four fan
Plus! Rate Arsenal players (and others) on Talentspotter
