"I am not good," Fabregas told the press after the game.
"We have to wait for tomorrow, but I hope I can wear the Arsenal shirt again this season.
"I fear the worst, which is that I have broken something. I do not think it is going to be good news, but still I hope there will be.
Fabregas says he knew immediately after he took the spot kick that something was wrong.
He said: "When I took the penalty, I was quite strong, but after when I went to get the ball, I could not walk any more.
"It is the fibula. I think I put my leg between [Carles] Puyol's when I was fouled, and kicked it."
He added that the match will live long in his memory: "Until the penalty, I was feeling quite good.
"It has been an amazing experience and I will remember it for the rest of my life."
Speaking after the match, Gunners boss Arsene Wenger conceded that it was too early to tell the full extent of his captain’s injury.
"I cannot give you any report yet. I've not spoken to the medical people,'' Wenger told ITV Sport.
Injuries to William Gallas and Andrey Arshavin meant that Wenger was forced into making two changes in the first half, before replacing Bacary Sagna with Theo Walcott after the interval. Consequently, having made all of their substitutions, removing Fabregas would have left Arsenal with ten men.
Wenger added: "I couldn't change anybody, I had to leave him on even though I wanted to take him off. In any case he wanted to stay on.'' <goal.com>