Vincent Kompany has vowed to return stronger from a further injury setback.
The Manchester City captain suffered the recurrence of a calf problem after appearing briefly as a substitute in City's 4-1 win over Sunderland.
"Today was a bad day for me," he said. "My mindset stays unchanged. I will fight to get what I deserve, my best years in football."
Kompany, 29, has been dogged by a succession of calf injuries and missed City's previous eight matches.
During that absence, City lost three times in the Premier League.
He played for just nine minutes against Sunderland and manager Manuel Pellegrini said the key defender's injury problems were difficult to work out.
"Vincent is not the best news," said Pellegrini. "He was ready to return. I did not want him to play the whole game because we have to play so many games, but he worked the whole week with normality.
"It is really difficult to understand what happened. We will see tomorrow with the doctor's report but it is the same injury, the same calf."