According to Belgian football expert Kristof Terreur, De Bruyne could be out for as long as two months.
He tweeted: “Kevin De Bruyne (27) has suffered a knee injury in training.
“Full extent not known as yet, but fears that he might be out for a while (as in +2 months).”
Manchester City are yet to comment on De Bruyne but the potential loss of the Belgian would be a huge blow to Pep Guardiola.
De Bruyne made a late return to pre-season after reaching the World Cup semi-finals with Belgium.
But he came off the bench on Sunday in City’s 2-0 win over Arsenal.
If the news on De Bruyne is confirmed he could miss games against Huddersfield, Wolves, Newcastle, Fulham, Cardiff and Brighton.
He would also miss the start of the Champions League and Carabao Cup.
But Guardiola will hope De Bruyne is fit to face Liverpool on October 7.
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