The Red Devils snatched an encouraging 1-1 draw at the Bernabeu, but will, likely, have much work to do to at home to the La Liga champions.
Former United star Ronaldo netted the equalling goal for the Spaniards and is widely regarded as their danger man.
But, although Fergie admits he is wary of the Portuguese star, he has told his team to focus on their own game and not worry about the attacker:
“My biggest concern is that he turns up.” He is quoted by BBC Sport.
“It is not something we should fear. If we worry about the danger Cristiano can give us we will forget some of the things we can do ourselves.”
Not many managers know Ronaldo better than Ferguson, with the Scot having signed the now 28-year-old in 2003.
After some scintillating displays at old Trafford, Real upped their interest in the versatile attacker, completing a world record £80m move for his signature during 2009.
As a result Fergie is almost certain of what to expect and hinted that plans are on place to attempt to nullify his threats:
“What do you expect when you play against a team with Cristiano in it?
“You expect problems during the match. We have to try to curtail that as much as we can and as best we can.
“The experience young Rafael had in the first half in Madrid hopefully helps him because he will be given the same task again.”
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