"Cesc will miss the remainder of the domestic campaign as he will be out of action for at least six weeks," a statement on the club's website (www.arsenal.com) said.
The Spain midfielder injured his right fibula in a collision with Barcelona defender Carles Puyol in Wednesday's 2-2 Champions League quarterfinal first leg draw.
He picked himself up to tuck away the resulting penalty for Arsenal's equalizer and hobbled through the final eight minutes before leaving the stadium on crutches muttering that he feared the worst.
A scan on Thursday confirmed that his pessimism was not misplaced but while the injury could not have come at a worse time for Arsenal as they try and reel in Chelsea and Manchester United, he should be fit for the World Cup finals.
Fabregas, who has been in sparkling form for third-placed Arsenal, has scored 19 goals in all competitions this season, and was patched up by Arsenal's medical department this week after receiving a kick against Birmingham City on Saturday.
Given the all-clear to play on Wednesday, Fabregas and his team mates were run ragged by Barcelona for an hour at the Emirates, but he gradually rallied his troops for an unlikely late revival that brought two late goals.
He would not have been able to play in the game anyway after a yellow card for a first-half tackle on Sergio Busquets, making his courageous performance even more remarkable.
"It was a gamble worth taking," Fabregas said after an epic encounter with his old club, although Wenger may well be questioning his own judgement now, especially with William Gallas and Andrei Arhsavin suffering calf injuries.
Arsenal face Wolverhampton Wanderers at home on Saturday after leaders Manchester United take on second-placed Chelsea at Old Trafford. With six games remaining Arsenal are four points behind United and three behind Chelsea.
