The Citizens have competed in Europe's top competition for the last seven seasons, making it to the round-of-16 stage four times and reaching the semi-finals in 2015-16.
Guardiola won the competition twice with Barcelona and thinks that City will need "to grow up" if the trophy is to make its way to the blue half of Manchester.
"We are Man City, we have to win our respect in Europe," he told reporters.
"I don't know if we are able to compete to win the titles. We are still in the process to grow up. We can do better than last season, but I don't know. It depends on our level. I know how complicated it is. Last season we did not win one game away.
"The quality is there. The only difference at Barcelona and Bayern Munich is that the players had played in the Champions League many more times before than the players at Manchester City right now. That's why I can't be sure if we will be able to make that step."
City begin their Champions League campaign tonight away at Feyenoord.