The Italian was sacked from his post at the Etihad Stadium in May following a shock defeat to Wigan Athletic in the FA Cup final, coupled with a poor season in which they failed to retain their Premier League crown.
City also finished bottom of their Champions League group last term, and while Mancini insists that they are still growing, he feels that they have some way to go before they can match the continent's elite.
"I would say City are a bit like Juventus. They are growing but are still a bit behind the big European clubs," Mancini told The Sun.
"To win the Champions League you need experience and the right squad. There aren't many games, so if you get two wrong then you're out of the running. In the Champions League last year, we had the toughest group. Now they have lost two important players in Carlos Tevez and Mario Balotelli.
"I do not agree with those who say German or even English clubs are dominant in Europe. The Germans have the benefit of a long winter break, while the English lose intensity as time goes on because they never stop playing. Bayern Munich are the team to beat, as they are full of stars, solid at the back and strong on the counter-attack. I still consider Barcelona to be the strongest team, though."
Mancini has since been replaced at City by Manuel Pellegrini.