David Silva has been ruled out of Manchester City's clash with Borussia Dortmund and is doubtful for the derby with Manchester United at the weekend.
Silva is a key figure for City, but could be forced to sit out arguably two of the club's biggest games of the season to date.
Silva played the entire 90 minutes of the 1-1 draw with Everton in the Premier League at the weekend, but has reported a hamstring complaint that has ruled him out of the Champions League clash with Dortmund.
The midfielder did not travel to Dortmund with the rest of the squad and will be monitored in Manchester ahead of the derby with United on Sunday. City must win the game to stand any chance of playing in the Europa League knockout stages.
Mancini said: "It's a hamstring. We don't know if he can recover for the derby. We will try.''
The Italian also insisted the date with United has not clouded his thinking for the Dortmund game. Mancini added: "We are a good team. We are a good club. We want to play well tomorrow and try to win. We have brought here all the players that are available. The other players that stay at home are injured.
"The players that are here will do everything to win this game. It will be difficult because I think in this moment Borussia are one of the best teams in Europe.''
The manager was wary of dropping into the Europa League, even though an elimination from Europe at this stage could cost the club a place in the second pot for next season's Champions League draw.
He said: "It could be difficult because in the Europa League you play Thursdays and you don't have a lot of days to recover for the Premier League, but we need to try to stay in the Europa League.''
City began the competition with much higher hopes and, given their resources, outside expectations were also greater but Mancini insists he is not embarrassed by the situation.
He said: "Embarrassment for what, I don't know, but we are disappointed because we wanted to go to the second stage this year. I think in football you need to learn. If there are other teams that play better than you and deserve to go through, we should accept this.
"If we didn't play well, Borussia and Real Madrid played better than us - we should accept this and we will try better next year.
"We still have a chance to play in the Europa League. We will do our best to try to win because only if we win can we continue in the Europa League. It won't be easy and we have a few players missing but we will do our best because everything is possible in football.''
If City lose to United at the weekend they will fall six points behind their arch rivals in the Premier League.
First-team coach David Platt had already warned that City's resources are being stretched to the limit - with eight players now ruled out of the game in Germany.
Aleksandar Kolarov limped off in Saturday's 1-1 draw with Everton because of a groin injury while Jack Rodwell, James Milner, Gael Clichy and Micah Richards all remain sidelined. In addition, Kolo Toure, who was not named in City's European squad, is ineligible and Yaya Toure, who has collected three yellow cards in the Champions League, is suspended.
"With everybody we have got on the treatment table, we are not going to have much choice," Platt said. "But the fortunate thing is that Dortmund is a Tuesday night game and we have an extra day to recover because the derby isn't until Sunday.
"Four days is enough to recover. You don't grumble about that, but we haven't got an advantage over United. At the end of the day, they have already qualified and they can pick any team they want against Cluj."