Maurizio Sarri insisted this week that Juventus and Manchester City are favourites for this season's competition, though Guardiola disagreed with the claims at Italy's 'Festival dello Sport'.
In an interview alongside Napoli manager Carlo Ancelotti, Guardiola remarked: "Manchester City can't be considered the favourite for the Champions League.
"Our history tells us that a semi-final is the maximum we could get. I don't know if we are ready.
"We should be very, very good to be favourite. Juve, for example, are getting closer and closer.
Last season, City were knocked out by Liverpool in the quarter-finals despite being one of the favourites to lift the trophy.