The Manchester United hero says the Spanish club will fear the firepower of the English giant's front line.
"Both sides seem to have the same strengths and weaknesses at the moment," he told Goal.com. "I was at Old Trafford the last time these sides met when Ronaldo scored a hat trick in a high-scoring and close tie. I can see it being high scoring again and perhaps just as tight over two legs."
McIlroy admitted that the firepower Real Madrid brings to the table should be enough to worry Manchester United, but pointed to the return of Nemanja Vidic for United as a reason for United to be hopeful.
"The Brazilian Ronaldo scored a hat trick that night in Manchester and Cristiano Ronaldo will fancy his chances of getting on the scoresheet but don't forget Madrid are not a one-man band," he said. "I would be fearful for United's defense if the tie was next week but they will have Vidic back to his best by the time the games are played in February."
On the other side, Wayne Ronney and Robin van Persie will be the key men in attack, and McIlroy thinks they will have Madrid's defense more than a little worried.
"At the other end, Madrid will be very wary of Robin van Persie and Wayne Rooney. If anything, I think they have more of a glass jaw than United," he went on, before claiming that the tie was too close to call.
"I think there will be just one goal between them but it's too close to call who will progress. Like all United fans, I can't wait for the tie to come around."