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."
"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."
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.
"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?"
"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.
