It will be Rafa Benitez in the adjacent dugout instead of the sacked Roberto Di Matteo, and the City boss said: "Usually when one team changes a manager the game after for the opponents is very difficult. For us, I think it is more difficult.
"Chelsea is a good team with Di Matteo and will be a good team for Benitez. They have good players. Until three games ago they played fantastic football and were on the top."
The decision to sack Di Matteo has drawn near-unanimous criticism from his fellow managers, and Mancini is no different.
He said: "I am very sorry for Di Matteo because he won the Champions League three or four months ago - but this is our life.
"When we make this choice to become a manager we know it can also be difficult. It is difficult for him, but this is the manager's life."