Manchester City have been dealt a huge setback with Kevin De Bruyne fearful he will be out for at least a month with a knee injury that will force him out of next week’s Manchester derby.

De Bruyne was substituted in the 85th minute of City’s 2-0 Carabao Cup win against Fulham at the Etihad Stadium on Thursday night after opposing defender Timothy Fosu-Mensah landed heavily on his left knee.

The Belgium midfielder asked to come off immediately and subsequent tests by City’s medical staff have revealed the damage is serious enough to keep the player out for around a month and possibly up to six weeks.

De Bruyne is now likely to miss City’s next six matches at least, including next Sunday’s derby against Manchester United at the Etihad. He is also expected to be ruled out of this Sunday’s league game against Southampton, the Champions League tie at home to Shakhtar Donetsk three days later and matches against West Ham, Lyon and Bournemouth.

A longer six week lay-off would keep him out of a further four matches, including the league fixtures against Watford, Chelsea and Everton and Champions League tie at home to Hoffenheim.