The prospect of losing Mendy for the rest of the season severely weakens Pep Guardiola's strategy for the campaign as the left-back was a key part of his summer squad rebuild, with City paying £52m to Monaco for him.
In a brief statement on the official site, City revealed that Mendy travelled to Barcelona to see a specialist doctor, who today confirmed the extent of his injury.
CITY have confirmed Benjamin Mendy will undergo surgery after rupturing knee ligaments - meaning the France ace faces NINE MONTHS out.
"Benjamin will undergo surgery [Friday] in Barcelona, and everyone at the club wishes him a speedy recovery".
Bar makes 'Lynch,' 'Kaepernick' doormat with players' jerseys
We have flags that have flown overseas mounted inside", Burle said. "We have some people's fathers, grandfathers, uncles, aunts". Burle told KOMU he created the doormat to stand up for himself and members of his family who had served in the military.
The City boss was forced to play midfielder Fabian Delph at left-back in Tuesday's Champions League victory over Shakhtar Donetsk, with one eye already towards now bringing in a capable deputy for Mendy in the January window.
Asked if City may buy a replacement, Guardiola added: "We will see".
Despite the diagnosis, Mendy was able to keep his sense of humour on Twitter, saying he is "joining Injury FC on loan for a couple months".
He followed it up with: 'Thank you all for the warm messages since the game.