Nasri has been told he cannot play for two weeks, and that rules him out of games against Reading, Sunderland and Norwich and leaves him extremely doubtful for the meeting with Stoke on New Year's Day.
City face a fixture schedule of four games in eleven days over Christmas and New Year, meaning that Nasri's injury comes at the worst possible time for a team looking at that six-point gap between them and United at the top of the league.
The Frenchman was widely blamed for gifting United a winning goal in the recent derby game by hiding at the end of the defensive wall, but his response at Newcastle was superb - until he was injured.
Roberto Mancini is already shorter of attacking options as there is still a question mark of Mario Balotelli and his ... errr ... illness.
The Italian striker missed his second successive day of training yesterday on the day he decided not to pursue his case against City at a Premier League tribunal.
Balotelli dropped the case at the last minute and agreed to pay a £340,000 fine imposed by City at the end of last season for picking up too many red and yellow cards.