It is a second major injury setback for the 24-year-old since he joined City in 2017 after missing the majority of last season with cruciate ligament damage in his right knee.
City are already without Kevin De Bruyne, yet to return to first-team training, while Bernardo Silva has been ruled out of the trip to the London Stadium after picking up a minor injury while on global duty with Portugal.
City are also top of their Champions League group with just two matchdays remaining.
Speaking at his pre-match press conference, Guardiola said of Silva: "He can not play this weekend".
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"I remember when I arrived in England it was a top four, now it is a top six, so every year it is more hard".
"Maybe I will change my mind later but I am fully convinced in my mind here".
Playing in peak physical condition for the first time in years, City's record scorer Aguero reckons he is now able to carry out manager Pep Guardiola's pressing instructions more thoroughly.
"We're not going to spend anything". Ok, they are very good and they have good players but it's possible to beat them.
As temperatures dramatically drop in the nippy winter months, this season's Premier League title is set to hot up as the early contenders for England's top gong attempt to juggle the frenzied flurry of festive fixtures that are crammed into the schedule at this chaotic time of the year. "He did well at Malaga as well and he is going to do well at West Ham".