Kevin De Bruyne will be sidelined for up to six weeks.
The Belgian midfielder suffered the injury during City’s 2-0 win over Aston Villa on Wednesday.
He is expected to miss around 10 matches including the Champions League tie against Borussia Monchengladbach on 24 February.
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“The doctor said we’ll review the scan which we’ve done and it will be between four and six weeks out,” Guardiola said.
“It is a big blow but we have to move forward.
“I’m not saying anything nobody knows about how important it is, but unfortunately for him and all of us, he is out for an important part of the season. We have to find a solution as everyone is struggling and we have to adapt.”
Guardiola then went on to rant about Premier League’s decision to reject the five substitutes per match rule.
“To demand they are fit for 11 months playing every three days is impossible,” Guardiola said. “There have been injuries at all the clubs.
“We knew it was going to happen. We’ve tried to avoid it. We have more medical treatment than ever, better nutritionists, we tried to masseur as much as possible to take care of the players but they are human beings.
“These amount of games and competitions, at the end the bodies of the players say ‘it’s enough’.
“The players don’t want to get injured but there are injuries, it’s no secret. When we demand five substitutions, it’s for this reason. Why can we do it in the FA Cup but the Premier League we cannot? Is it a special competition?