Arsenal skipper Cesc Fabregas is out of their FA Cup tie at Manchester United.
The Gunners skipper suffered another hamstring injury in the defeat at Barcelona.
He said: "Fifteen minutes into the second half I felt a pinch at the back and knew the game was over for me."
The Spain midfielder, 23, will now have a scan to reveal the extent of the problem.
He missed the Carling Cup final and home draw with Sunderland after coming off with a tight hamstring against Stoke.
