Saturday's game pits two big-spending sides against each other with Chelsea, who have won three league titles since their 2003 takeover by Roman Abramovich, tipped by Mancini to add more while City, the world's richest club, await a first trophy since their 2008 takeover.
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"I think that Chelsea is the best team in this moment," the Italian, whose side trail the Londoners by seven points in fourth place, told a news conference on Friday.
"I think that probably they will win the Premier League easy because it's a strong team and they play together for many years and they have fantastic manager."
Mancini was preparing to host the free-scoring champions, who have scored 21 goals in their first five league games, with a severely depleted team.
"We don't have defenders for tomorrow," he said.
"If you are a defender you can go on," he joked to reporters before returning to his serious problem. "We only have 11 players that can play 100 percent."
"I'm disappointed having all these players injured at this moment, it's an important moment for us."
The value of players on his injury list runs to tens of millions of pounds.
Mancini reeled off City's problems with a grim face.
Micah Richards: "Injured." Joleon Lescott: "Not ready to play 90 minutes." Wayne Bridge: "Injured." Aleksandar Kolarov: "Injured." Jerome Boateng: "Not ready to play 100 percent."
He said he would talk to Lescott and Boateng after Friday's training session but if they were not fit he said he did not know what to do. Mancini ruled out playing a midfielder like Gareth Barry at the back.
Facing the league leaders when they are in such great scoring form when your team is short at the back could spell trouble but Mancini remained optimistic.
"When you score so many goals for four or five games a game arrives where you don't score," he said.
"I hope (it can happen here). Why not?"
He has some reason for optimism as City beat the Londoners twice last season with Carlos Tevez scoring in both games.
With so many players sidelined it was with some relief that Mancini pointed out that having been knocked out of the League Cup by West Bromwich Albion in midweek at least City now had one less competition to think about.
"I think with the problem we have at this moment we couldn't do four competitions, three competitions we can do," said Mancini, whose side face Juventus in the Europa League next week.
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