Arsenal captain Cesc Fabregas has been ruled out for up to three weeks with a hamstring problem and looks set to miss the showdown with Barclays Premier League leaders Chelsea on October 3.
The Spain midfielder suffered the injury as he netted a freak goal at Sunderland on Saturday, the ball kicked into him by Anton Ferdinand and it looped back into the goal.
Fabregas, 23, had just been finding his form having returned late after reaching the World Cup final.
With Theo Walcott, Robin van Persie and Nicklas Bendtner all still sidelined, the loss of another key man is an additional blow to manager Arsene Wenger.
Fabregas used his personal Twitter account on Monday night to reveal he hoped to be playing again in two weeks, saying: "I have some fluid but nothing bad in the muscle."
However, the official club line on Tuesday was more cautious.
"Arsenal Football Club have confirmed that Cesc Fabregas will be out for two to three weeks," a statement read.
"The Spanish midfielder gave the visitors an early lead at Sunderland on Saturday but then picked up a hamstring injury. He was substituted just before the half-hour. The extent of the injury was discovered after a scan on Monday afternoon."
Fabregas would not have been included in the squad for Tuesday's Carling Cup third-round tie at Tottenham and will also miss Saturday's visit of West Brom, as well as next week's trip to Partizan Belgrade in the Champions League, and it remains to be seen whether he has recovered in time to face Chelsea at Stamford Bridge on October 3.