The Italian feels his side face a hard task retaining their crown, insisting as many five teams can win the competition, whilst stating his desire to keep his current strikeforce
The Blues ended their 44-year wait for a top-flight league success last season, dramatically pipping local rivals Manchester United on the final day.
And Mancini has stressed the importance of everyone at the club staying focused, insisting up to five teams can challenge their supremacy.
"We did a good job for the last two years and I hope we can do a better one in the next five," Mancini told the club’s official website.
"But we cannot rest or start thinking that because we won the title that we are the best.
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"I think there are four or five teams that can challenge but now, before the transfer window is closed, I think [Manchester] United and Chelsea will challenge us for the title."
The former Inter Milan boss also stated his desire to keep hold of Sergio Aguero, Mario Balotelli, Edin Dzeko and Carlos Tevez, despite the club's four first-team strikers being linked with move away.
"I think such speculation is normal, we have four top strikers and all the other teams in Europe would like strikers like them,” he added.
"After January last year the problems with Carlos were finished. He came back to Manchester and his behaviour was good. He played a lot of games and scored important goals that helped us win the title. Now he has started the pre-season training very well."