Ilkay Gundogan's season could be over after Manchester City announced the midfielder suffered cruciate ligament damage in midweek.
The Germany international fell awkwardly in the first half of City's victory over Watford at the Etihad Stadium on Wednesday and limped off in clear distress soon after following an unsuccessful attempt to play on.
City are not yet able to put a timescale on the length of lay-off facing the 26-year-old, who will undergo knee surgery, but it seems unlikely he could feature again in the 2016-17 campaign.
The club said in a statement: "Manchester City can confirm Ilkay Gundogan has sustained a cruciate knee ligament injury. Gundogan will now be assessed further to discover the exact extent of his injury."
It is the former Borussia Dortmund player's second serious knee injury of the year having dislocated the patella of the same joint playing basketball prior to joining City last spring. He consequently missed the first six games of the season for his new club.
The £20million signing has since made 16 appearances for City, scoring five goals, and seems to have settled in well.
Manager Pep Guardiola spoke about the player when asked at a press conference to preview Sunday's Premier League game against Arsenal.
Guardiola said: "It is so, so difficult for him. We are sad for him. We are going to miss him a lot.
"But it is what it is. He's unlucky, sometimes football is like this. It was an unlucky situation.
"Now we need to help him to feel we are there and wait and come back safe. That is going to happen because he's going to be operated on by the best one and be back as soon as possible and the most important thing is his future."
With Gundogan now out of the picture, Yaya Toure's involvement is likely to increase.
Toure is back in the first-team reckoning after being frozen out by Guardiola earlier in the campaign following a spat with the Ivorian's agent.
Toure was left out of City's Champions League squad for the group stages but could be reinstated for the knockout rounds.
Guardiola said: "Now he has come back I have seen him play like he can and he was (doing) when I met him in Barcelona. He's a player with no doubt about his quality.
"Now in this moment he is maybe going to have more minutes than before. That's why you have a squad big enough.
"Of course we have other options. We have Fernando, Aleix (Garcia), Kevin (De Bruyne) can play in that position as well. In the next game Fernandinho is coming back (from suspension).
"During the season these things happen. You don't expect to be all season with all the players fit - but we want the injuries as short as possible and in Ilkay's case that is not going to happen."