The Barclays Premier League leaders face a test of their title credentials with tough fixtures against Chelsea and Arsenal before Christmas. January provides three clashes against Liverpool - including the two-legged Carling Cup semi-final - a visit from Tottenham and the start of the FA Cup defence against arch-rivals Manchester United.
Mancini said: "We have done well but the season is long. Now we have two difficult games against Chelsea and Arsenal. I have said before the next two months will be important months."
City will also have to make do without their midfield inspiration Yaya Toure, as well as his defensive brother Kolo, early in the new year due to their involvement in the African Nations Cup with Ivory Coast.
The Toures will return before City begin their Europa League campaign in mid-February and Mancini hopes his team have asserted their dominance by then.
"Yaya is an important player for us - we don't have any other players like Yaya," Mancini added.
"We will probably lose an important man for one month at a crucial moment.
"For this reason I think if we do well in January, and we are top after January, it will be difficult to lose."