Manchester City boss Pep Guardiola fears he could be without Sergio Aguero for a significant length of time after the striker suffered a "bad" muscular injury during the 2-1 win over Chelsea.
Aguero hobbled off 13 minutes from time and was replaced by Gabriel Jesus as City came from behind to beat Chelsea at the Etihad Stadium.
City hit back after N'Golo Kante's 21st-minute strike with goals from Kevin De Bruyne and Riyad Mahrez to take all three points, but now face an anxious wait to see how serious Aguero's injury might be.
Guardiola told Sky Sports: "I think Sergio will be bad.
"The doctor will have to look, he thought it was a kick, but it's maybe he has strained something. But we will see tomorrow.
"The feeling is if it is muscular, we are going to lose him in the toughest period of the season, but it is what it is.
"We have young players and we will try."
Guardiola also revealed that midfielders Rodri and David Silva had suffered cramp during the win over Frank Lampard's side.
The City boss added: "With Rodri and David Silva, they were problems with cramp, and they were tired.
"Rodri is a month and a half without playing games.
"David after the international break didn't train too much and after these games you need some rhythm in your legs.
"These games are so demanding and that's why it happened."