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.
Clearly, he knows it's a serious injury and the official updates from City in the coming days will likely confirm the sad news.
The agent of Manchester City attacker Kevin De Bruyne is confident that the Belgium global will not be out of action for too long.
De Bruyne was City's Player of the Season in 2017-18 after inspiring Pep Guardiola's side to Premier League and Carabao Cup glory but suffered a seemingly damaging setback in training on Wednesday.
It's said to be a very similar injury to the one he picked up against Everton in 2016, which saw him sidelined for over two months.
City became the first team ever to win 14 successive English top-flight games when they triumphed 2-1 at Old Trafford last December.
All Or Nothing: Manchester City will take viewers on an exclusive journey through the whole of Manchester City's 2017-18 season; from the world-leading training facilities at the City Football Academy, to interviews with the manager, boardroom meetings and other surprise moments across the season. "Obviously it's a big loss but we've got more than enough cover".
City midfielder Ilkay Gundogan said of De Bruyne: "He played an incredible season. But as long as his ligaments are not torn we can remain hopeful he'll make a quick recovery".