Arsenal skipper Gallas out for three weeks
The defender went down in agony off after hurdling a 24th-minute challenge from Roque Santa Cruz in Sunday's 1-1 Barclays Premier League draw.
He immediately called for assistance from the bench and, a few minutes later, hobbled off to be replaced by Philippe Senderos.
"He has done his groin, I knew it straight away," manager Arsene Wenger said on the club's official website.
"He will be out for three weeks."