Vincent Kompany is a doubt for the Manchester derby after being ruled out for at least a month with a groin injury.
The Manchester City captain had to be substituted during his side's 4-0 opening-day victory over Newcastle on Monday, and manager Manuel Pellegrini has confirmed he is facing a minimum of four weeks on the sidelines.
City face Manchester United at the Etihad Stadium on September 22, meaning the Belgium international is facing a race against time to be fit for the clash against the champions.
"I prefer the doctor has the final word on this but I think he will be out for at least one month," Pellegrini said ahead of the clash with Cardiff City on Sunday.
"If we do strengthen (at centre-back) it will not just be because of Vincent Kompany’s injury. We have a very good squad and we see what happens.
"Today or tomorrow we will know exactly how long Vincent will be out for."
Kompany joins fellow defender Matija Natasic on the sidelines after the Serbian missed the Newcastle game with an ankle injury.