Vincent Kompany is set to be side-lined for at least four weeks after picking up a groin injury against Newcastle.
The skipper limped off after 71 minutes during the convincing 4-0 win against the Magpies on Monday night.
"I prefer the doctor has the final word on this but I think he will be out for at least one month," confirmed Manuel Pellegrini.
"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 will see what happens.
"Today or tomorrow we will know exactly how long Vincent will be out for."