The Spaniard played 66 minutes of City's 5-2 Champions League win at home to CSKA Moscow on Tuesday night but is now facing a spell on the sidelines.
"I don't know how many weeks at the moment, but it could be three or four," confirmed City manager Manuel Pellegrini.
Pellegrini is currently without skipper Vincent Kompany and there are doubts over the availability of Fernandinho and Matija Nastasic for the game at Sunderland on Sunday.
"It (the Kompany injury) was diagnosed as being a five-week problem," said Pellegrini. "That was three weeks ago, so he should be fine in another two weeks.
"We hope if he continues this way he will be fine."
Pellegrini was unaware of reports that the Belgian Football Association was planning to send a physiotherapist to Manchester to assess Kompany.
There is general concern over the 27-year-old's fitness after a number of muscle injuries in the past two years.
"I don't know about that," Pellegrini said.
City are also still without striker Stevan Jovetic due to a calf injury ahead of the weekend trip to the Stadium of Light.
Watch Sunderland take on Manchester City live on Sky Sports HD1 (2.05pm kick-off) during Ford Super Sunday.