Arsenal closed the gap on Manchester United to just one point at the top of the Premier League table courtesy of Sebastien Squillaci's early goal against Stoke, but the victory came out a cost with both Walcott and Fabregas limping out of the action.
Arsenal boss Arsene Wenger immediately ruled Walcott out of the final at Wembley after he had to be stretchered off in the second half of the win with a sprained ankle.
By that time, Fabregas had already been replaced after exiting the action early with a hamstring strain and Arsenal's captain will have the injury assessed over the next 24 hours.
Arsenal's captain has had a history of hamstring problems but the Spanish star refused to rule himself out of the clash against Birmingham, saying on Twitter: "I don't know if I'll make Sunday or not, but all I know is that from this moment to Sunday I won't sleep if it's necessary. I've waited too long to captain a final for Arsenal and I won't give up till the last second."
Wenger is already waiting on the fitness of striker Robin van Persie and defender Laurent Koscielny after the duo were forced to miss the win over Stoke with hamstring and back problems but he was delighted with the overall performance of his side.
He said: "With the number of games we played, we still did not make a mistake.
"We were less sharp creatively, but you can feel that the team did not want to make a mistake and that is a very positive sign for me. It means your team is really hungry for success. The game was massive for us."