Ronaldo is Madrid's biggest threat and he will be out to upset his former club when returning to Old Trafford for the first time since his record-breaking switch to the Bernabeu.
"My biggest concern is that he turns up!" joked Sir Alex. "What do you expect when you play against a team with Ronaldo in it? You expect problems during the night. We have to try and curtail that as best we can.
"It won't be easy because he does it every week, it's not an accident about the lad. The experience young Rafael had in the first half in Madrid hopefully helps him because he'll be getting the same task again. I don't think it's one we should fear. If we go in worrying about the damage Cristiano can do then we'll forget some of the things that we can do ourselves."