De Bruyne left training today on crutches and the club will discuss sending the Belgian to Catalan doctor Ramon Cugat, who Guardiola has leaned on in the past.
De Bruyne was City's player of the season last term, scoring 12 goals and providing 21 assists as his side won the Premier League and EFL Cup.
A similar recovery time this time round would see the Belgium worldwide ruled out until at least November, but with the severity of the injury unknown, City manager Pep Guardiola will be left sweating over the results of his medical examinations.
Due to being given three weeks off following the World Cup he did not play a role in the Community Shield win against Chelsea but came on for a cameo role of half an hour in the 2-0 opening Premier League victory over Arsenal last Sunday.
This would be a huge blow to City's hopes of retaining their title, with De Bruyne having been so instrumental for the Citizens.
Some Liverpool fans on Twitter have responded to reported news of an injury to Manchester City midfielder Kevin De Bruyne.
Clearly, he knows it's a serious injury and the official updates from City in the coming days will likely confirm the sad news.
Manchester City will be without the playmaker for the foreseeable future but have adequate cover in Ilkay Gundogan, David Silva and Bernardo Silva.