David Moyes admits he could be facing a selection headache in defence for Tuesday's Champions League quarter-final tie against Bayern Munich.
Rafael was withdrawn at half-time in the 4-1 beating of Aston Villa due to injury after Antonio Valencia, another option at right-back, was unavailable. With Patrice Evra suspended for midweek, at least Alex Büttner got through the 90 minutes, even if he stayed down for a spell after winning a brave header during the build-up to Juan Mata's goal.
"With Rafael, it's an injury and we need to check it out," revealed Moyes. "Valencia had a bit of tendinitis in his knee, which is why he wasn't involved. He was probably one I would have put to full-back if we had lost one, so we knew we'd be short if that was the case.
"The young boy Guillermo Varela might have got on the bench but he was injured as well so we had to juggle it around. We have injuries but we will probably know more about them tomorrow. I've just got to hope that Rafa's injury isn't too bad."