The Serbia international will come face-to-face with the star winger if Roberto Mancini selects him as part of his defence when the champions of England and Spain face each other on Tuesday evening.
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The two sides will meet at the Santiago Bernabeu in the first round of fixtures in a group that also contains Dutch and German champions Ajax and Borussia Dortmund.
Kolarov believes that Ronaldo's affiliation with Manchester United will only fuel his desire to beat one of their fiercest rivals in Madrid.
"He [Ronaldo]'s a special player - with Messi he is the best player in the world," Kolarov told the Daily Star.
"So to play against someone like that will be a big test. He played for Man United too so he will want to score against us.
"But I'll be confident, because City can go to Madrid with confidence. It should be a great night for the club."