Manchester City boss Manuel Pellegrini admits they're struggling to get to the bottom of Matija Nastasic's knee injury.

The centre-back has been out much longer than initially anticipated and the former Malaga boss admits it'll be weeks for him to return to the first-team.

The Chilean said: "He continues with some pain in his knee. He has at least a couple more weeks to recover.

"Of course we are concerned because the doctor doesn't know what happened with him.

"He made all the exams that he needs but we don't know what happened with him.

"We are taking other opinions. The doctor is in charge of that.

"The player feels a pain inside the knee but nobody knows what the pain is."