"He's got a few stitches under his lip and he's lost a tooth. He was dazed rather than concussed but if we'd waited for him to come round we would have played 10 or 15 minutes (with ten men) and you can't afford that in such a big game. So we took him off."
Rooney was withdrawn in the second half, moments after scoring United's equaliser.
"Wayne got the same knock as he got last week, straight on the hip bone," said Sir Alex.
"It takes a while for that to clear because when you get a bang on it, it's very painful. I'm hopeful he will be alright for Tuesday's match against Barcelona.
"Other than that, I think everyone's okay."