David Silva is likely to miss Manchester City's FA Cup semi-final against Chelsea on Sunday after going off injured in their 2-1 derby win at Old Trafford.
The Spain international sustained a hamstring problem in the closing minutes against Manchester United and was replaced by Joleon Lescott.
And City manager Roberto Mancini said: "Maybe it is not so bad, but I don't think he will be ready for Chelsea."
Victory was secured by goals from James Milner and substitute Sergio Aguero, reducing the gap to the league leaders to 12 points.
However, Mancini insisted the title race is over, adding: "The championship is finished."
But the Italian said City will not so far behind United again next year and reiterated his belief they can reclaim the league title.
And he compared the big gap to the league leaders to the situation in other European leagues.
"In football this can happen," he said. "In Spain, in Germany - Real Madrid and Barca (are) too far (apart), Bayern Munich and Dortmund too far.
"There are some years when maybe you lose stupid points like us against QPR, Liverpool at home. It that moment we lost five or six points and after that it was difficult."
Mancini said City lacked the strength in depth to challenge when key players like Aguero, captain Vincent Kompany and midfielder Yaya Toure were absent.
He explained: "This season we had some problems with some important players injured - Aguero, Vinny, Yaya - for African Cup. We are not a team that can lose three or four important players like this."
But he felt his side merited their second successive league victory at Old Trafford, saying: "We deserved to win because we played better. We played good football."