Manchester City playmaker David Silva could be out of action for up to a month with a calf injury, manager Manuel Pellegrini said on Friday.
The Spain international, who had already missed a month of this season with a thigh injury before returning in early October, came off midway through the second half in Tuesday's 5-2 Champions League victory over CSKA Moscow.
"Silva has a problem with his calf so he could miss three or four weeks," Pellegrini told a news conference ahead of Sunday's trip to Sunderland (1405 GMT) in the Premier League.
He said midfielder Fernandinho and defender Matija Nastasic face late fitness tests.
City remain without captain Vincent Kompany, who has missed their last six games with a thigh injury, although the Belgian could be back soon.
"It was diagnosed as being a five-week problem," said Pellegrini. "That was three weeks ago, so he should be fine in another two weeks."
Pellegrini's side are currently fifth in the league but a win against struggling Sunderland will put them three points behind leaders Arsenal who visit Manchester United later on Sunday (1610 GMT).
(Reporting by Sam Holden,; Editing by Toby Davis/Alan Baldwin)