The Gunners captain had been a doubt for the game which ended 2-2 at the Emirates Stadium after suffering severe bruising to his knee and leg at Birmingham.
However, after coming through a fitness test in the warm-up, Fabregas returned to lead the side against his boyhood club - and played a pivotal role in their comeback after falling 2-0 down to a brace from Zlatan Ibrahimovic which looked to have all but killed off the tie.
During the closing stages, after substitute Theo Walcott had pulled a goal back, Fabregas - who would have missed the second leg against his old club anyway after being booked in the first half - was bundled over by Carles Puyol and awarded a penalty.
It was during that collision with the Barcelona captain, who was shown a red card by Swiss referee Massimo Busacca, that Fabregas suffered the latest problem. However, while he will miss the rest of the domestic season, the 22-year-old should still be fit for the World Cup with Spain.
An Arsenal statement read: "Following a scan the club can confirm Cesc Fabregas has suffered a small crack in his right fibula as a result of the collision with Barcelona defender Carles Puyol during Wednesday evening's match.
"As a consequence, Cesc will miss the remainder of the domestic campaign as he will be out of action for at least six weeks. Everyone at the club wishes Cesc a full and speedy recovery."
( source:PA Sport)
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