The club sacked the Italian in favour of Manuel Pellegrini after the Chilean's success in Europe, but the coach believes the Blues will struggle again
The Chilean has a strong record in the competition, reaching the semi-finals with Villarreal in 2006 while two last-gasp goals saw them knocked out at the quarter-final stage to eventual runners-up Borussia Dortmund last season.
In contrast, Mancini was dismissed after failing to take City beyond the group stages in both attempts and feels the club will suffer a similar fate this term.
"I would say City are a bit like Juventus. They are growing but are still a bit behind the big European clubs," he told La Gazzetta dello Sport.
"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."
Following the all-German Champions League final last season, some have questioned whether the Bundesliga has overtaken the likes of La Liga and the Premier League as the strongest in Europe.
But Mancini, despite praising Bayern Munich's squad, still feels Barcelona are the team to beat in the Champions League.
"I do not agree with those who say German or even English clubs are dominant in Europe," he continued.
"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 counterattack. I still consider Barcelona to be the strongest team, though."