Manchester City captain Vincent Kompany could be fit "for the last part of the season", says manager Manuel Pellegrini.
Kompany, 29, who is out with a calf injury for the 12th time since the start of 2011-12, is trying to work out the reasons for his injuries.
The Belgium defender had been expected to return at the end of January.
"At this moment it is difficult to tell you an update about that. Maybe not so soon," says Pellegrini.
Kompany, who also captains his country, is in danger of missing Euro 2016 if he does not play again this season.
Manchester City have only conceded one Premier League goal - in a 2-1 win over Norwich - while he has been on the pitch in nine top-flight games this season.
However in the 11 games he has missed, they have only kept one clean sheet.
Fellow City centre-back Eliaquim Mangala is also injured, but City are not planning to sign anyone, according to Pellegrini.
"We have Martin Demichelis, Nicolas Otamendi, Bacary Sagna, who can play in a central defensive position, and Cameron Humphreys, who is a young player who featured in pre-season with the squad," he said.
"Mangala will return soon. So, at this moment, we are not thinking about making a change."