De Bruyne was injured on Wednesday in training and is set for a spell on the sidelines, and it's unknown if he will be back in time for the first Manchester derby of the season.
The extent of the injury is not yet known but the staff at Man City are reportedly fearing that he could be ruled out of action for more than two months.
However, with the season in its infancy and the transfer window closed, the Champions have now confirmed that their star midfielder is undergoing tests after sustaining an injury to his right knee in training this afternoon.
According to www.metro.co.uk, De Bruyne faces around two months out after suffering the injury when he caught his studs in the turf before leaving the training ground on crutches.
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He also has Bernardo Silva and Ilkay Gundogan, who were both brilliant in the 2-0 win over Arsenal on the weekend.
"He's very important - a key player for us, so we hope he is able to return as quick as possible".
Gundogan and Fernandinho were speaking at the world premiere of All or Nothing: Manchester City, available on Amazon Prime Video from Thursday.