Arsene Wenger expects to be without William Gallas for three weeks after the Arsenal captain injured his groin during Sunday's 1-1 draw with Blackburn Rovers.
The injury-plagued Frenchman limped off during the first half at Ewood Park following a challenge from Rovers striker Roque Santa Cruz.
The 30-year-old former Chelsea defender was replaced by Philippe Senderos and Gunners boss Wenger has revealed he doesn't expect Gallas to be back in action until next month.
"He has done his groin, I knew it straight away," said Wenger.
"He will be out for three weeks."
Gallas now faces a race against time to be fit for the north London derby with Tottenham on September 15.
The former Marseille defender has started just 23 Premier League games following his move from Chelsea last summer.