Sky Sports relayed the news:
Mendy suffered the injury during last weekend's 5-0 win over Crystal Palace.
Per Goal's Sam Lee, Guardiola is anticipating he will be back for the business end of the UEFA Champions League, should City progress that far:
Mendy is trying to maintain a positive outlook amid the disappointing news:
Losing the 23-year-old for the majority of the season will be a big blow to City as he is not only an excellent player, he's also their only natural left-back.
Danilo can provide cover there, but he's also the back-up right-back should Kyle Walker be absent.
Guardiola may be forced into deploying midfielders Fabian Delph or Fernandinho there, though that would hardly be ideal.
City have an overwhelming amount of firepower going forward, but Mendy's injury leaves them weaker at the back and vulnerable on the left flank, which could jeopardise their title chances.