"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 said.
The Spain midfielder injured his right fibula in a collision with Barcelona defender Carles Puyol in Wednesday's 2-2 Champions League quarter-final first-leg draw in London.
He picked himself up to tuck away the resulting penalty for Arsenal's equaliser and hobbled through the final eight minutes before leaving the stadium on crutches muttering that he feared the worst.
A scan on Thursday confirmed 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.
"I hope he recovers as soon as possible so we can start enjoying his play again and he can go to the World Cup because he will be a very important player for us," Barca captain Puyol told a news conference on Thursday.
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.
WALKING WOUNDED
He would not have been able to play in the second leg 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 manager Arsene Wenger may well be questioning his own judgement now, especially with William Gallas and Andrei Arshavin suffering calf injuries.
The pair have been ruled out for at least three weeks, with Gallas suffering a recurrence of a calf problem that has plagued the Frenchman since February 10.
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.
Wenger, who will hope his walking wounded can keep the team's title-tilt going, also have defender Gael Clichy (back) and midfielder Denilson (groin) struggling for Saturday.
"At the moment, we are like an army who have come back from a big battle," Wenger said.
"We have some bruises but we need to recover and then go to the next battle. Who will be available for the next one? I have to wait 24 hours more."
NEWS:Gunners regroup after battering by Barca
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