London - Manchester City midfielder David Silva will miss Sunday's derby against Manchester United and could be out of action for up to a month with a knee injury, manager Manuel Pellegrini said Friday.
Silva was injured during the early stages of holders City's 2-0 League Cup defeat at home to Newcastle United on Wednesday after a clash with the Magpies' Ryan Taylor.
"Manuel Pellegrini confirms that @21LVA will miss Sunday's game. Will be out for 3-4 weeks," City said on Twitter on Friday.
Silva is now also out of City's potentially decisive Champions League group match against CSKA Moscow and the Premier League fixture away to Queens Park Rangers.
He is also doubtful for Spain's upcoming Euro 2016 qualifier against Belarus and a friendly with Germany.
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"David has a problem in his ligament," City manager Pellegrini added at a news conference on Friday.
"Maybe he will be out around three weeks so he will not be available for the derby.
"He is a very important player but I think we have a squad and we have to replace him with another player."
Midfield star Yaya Toure came off as a precaution during the Newcastle defeat due to a groin problem but Pellegrini was optimistic the Ivory Coast international would feature in the derby.
"Yaya has a small problem. We will see him on Saturday but I think he will not have any problems," the Chilean boss said.
Meanwhile Samir Nasri appears to have made a successful return to action in midweek after seven games out following groin surgery.
Premier League champions City have gone three games without a win in all competitions and could be nine points behind leaders Chelsea by the time they kick-off against United at Eastlands on Sunday if Jose Mourinho's table-toppers beat struggling QPR on Saturday.