The City left-back’s absence was confirmed by Pep Guardiola at the pre-West Ham press conference and means he is unlikely to be available until mid-February at the earliest.
Mendy was forced to withdraw from the France squad during the international break and underwent surgery on his knee.
Said Pep: “Benjamin will miss between 10 and 12 weeks.”
The injury will not mean City delve into the transfer market in January with Fabian Delph and both likely to deputise for Mendy is his absence.
On 14 November, the City left-back tweeted: “Other knee was jealous, but the operation went well and it’s all good now be back soon guys.”
Mendy missed seven months last season after injuring his other knee in a home game with Crystal Palace.