David Silva
David Silva and Yaya Toure are doubtful for Manchester derby at the Etihad. Getty

Manchester City have suffered a massive blow ahead of Sunday's derby against Manchester United after the star midfield duo of David Silva and Yaya Toure limped out on Wednesday.

The Citizens were knocked out of the Capital One Cup by Newcastle United at the Etihad as the holders crashed out of the competition in the fourth round. Rolando Aarons and Moussa Sissoko's goals were sufficient for the Magpies to seal a victory over Manuel Pellegrini's side.

Silva picked up a knee injury while Toure is suffering from a groin problem. The former Real Madrid boss is sweating over the fitness of the key midfield duo and the Chilean claims both Silva and Toure could miss the weekend league clash against United at the Etihad.

"We will see tomorrow with the doctor and I can't tell you at this moment. David has a problem with his knee and I don't know how serious it is," Pellegrini said.

"Yaya was a little bit tired in his groin, so I didn't want to risk him any longer."

"There was no reason why David could not play. We played on Saturday, he had four days to recover, David was perfect to play, so there was no reason not to play him. He was prepared to play."

"Maybe he was not going to play the whole game and my idea was to change him later for Samir Nasri," he added.

The Premier League champions are without a win in the last three matches played in all competitions. Last midweek, City saw their Champions League clash against CSKA Moscow end in a draw before suffering defeats against West Ham United in the league and Newcastle in the Capital One Cup on Wednesday.

Pellegrini has admitted that he is worried with City's form going into the Manchester derby on Sunday.

"Of course, we must be worried. We didn't win the three games we played this week. We must be worried about that, but we must find a solution, we must address it," the City manager said.

"My feeling is that we are not playing well. We are in a difficult moment. There is a lack of trust. We conceded two easy goals and we did not score from the chances we had. We are conceding goals too easily and not scoring, so when that happens, there is a lack of trust."

Meanwhile, Louis van Gaal will welcome his skipper Wayne Rooney on Sunday after the England international completed his three match suspension for his tackle on West Ham's Stewart Downing.

Rooney was reportedly doubtful for the City tie, along with Radamel Falcao. However, it is believed that both United strikers are likely to be fit for the clash against the Premier League champions.