The Citizens head into the game after having suffered back to back Premier League defeats at the hands of Leicester City and Tottenham Hotspur.
Chelsea, meanwhile, were beaten 2-1 by Paris Saint-Germain in the Champions League in midweek despite producing an admirable display in the French capital in the first leg of their last 16 clash.
Mills feels that winning the FA Cup after such a disastrous start to the season would represent a significant achievement for Chelsea.
And the former defender says that the game could end up being something of a banana skin for City at Stamford Bridge.
Writing in his blog for Sportlobster, Mills said: “It’s a huge game for Chelsea and Man City in the fifth round of the FA Cup. There’s a very real possibility that the winner will go on to lift the trophy.
“Chelsea need to make use of every opportunity to improve and play themselves back into form. A trophy at the end of such a tumultuous season would be exceptional.
“For City, this game could be something of a banana skin. Imagine they were to crash out of the FA Cup and lose in Kiev next week. That would be two more trophies gone for City, coupled with a poor run of form in the Premier League.
“In that respect, it’s a massive couple of weeks now for Man City that could define the end of Pellegrini’s reign one way or another.”
Chelsea’s defeat by PSG in midweek was their first loss since the appointment of Guus Hiddink as Jose Mourinho’s successor at Stamford Bridge back in December.
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