The Premier League champions meet Stoke at the weekend but then face the daunting task of travelling to the Bernabeu to face Real Madrid in their opening Group D clash.
And Kolarov, 26, knows just how crucial stopping Ronaldo will be if City are to get a result in Spain, saying: "Ronaldo is something different. Everyone knows about him, there's nothing much more that you can say about him. He's a special player - with Messi he is the best player in the world. So to play against someone like that will be a big test."
He went on: "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. "We are the champions of England and they will know it will not be an easy night for them as well. Everyone at Man City will look forward to going there."
City were eliminated in the group stages of last season's Champions League, and they face a tough task this time around with their group being completed by Ajax and Borussia Dortmund.
The Blues ultimately paid the price for a slow start that saw them pick up one point from their first two games, and Kolarov knows they cannot afford a repeat.
"We want to do better in the Champions League and qualify but again we have been given a really tough group. This time we need to start better than we did last year," he said.
- Real Madrid
- Champions League