Vincent Kompany has suffered a groin injury but the seriousness of the problem is still being assessed by Manchester City's medical staff.
The City skipper left the pitch two minutes into injury time of the EFL Cup victory over Swansea City on Wednesday night in his first game in four months.
The defender left the pitch after stretching to try to stop Gylfi Sigurdsson's consolation goal and punched the ground in frustration as he stood up.
A statement released by City read: "No date has yet been set for his return. The positive for Kompany and City is that the injury is not a recurrence of the calf problems that disrupted his progress last season.