David Silva will miss three to four weeks with a knee ligament injury he suffered in Manchester City's League Cup match against Newcastle.
Silva underwent a scan on Thursday after limping off after just nine minutes of City's 2-0 defeat.
Silva will now miss some crucial games including Sunday's derby against Manchester United as well as the midweek Champions League clash against CSKA Moscow.
"David has a problem in his ligament," the City boss told reporters. "Maybe he will be out around three or four weeks so he will not be available for the derby.
"David is a very important player but we have a squad and we will have to replace him with another player."