Aguero to miss Manchester derby
Aguero was expected to be out for around a fortnight after suffering a hamstring injury early in last week's Champions League defeat in Barcelona.
That made him a doubt for next Tuesday's Old Trafford clash anyway but Pellegrini has now admitted there is "no chance" of him making the short trip across town.
Aguero, who has scored 26 goals for title-challenging City this season, is now targeting a return in the game at Arsenal the following Saturday.
Pellegrini said: "We don't know yet, but maybe next week he will start working with the squad.
"I don't think the whole week, maybe at the end of the week he can be with the squad starting training."
When asked directly if the Argentinian, who scored the winner at Old Trafford last season, could face United, Pellegrini said: "For United, no, no chance."
Pellegrini, who was speaking at a press conference to preview this weekend's home game against Fulham, was also asked about fresh rumours linking Aguero with a move to Barcelona.
Pellegrini said: "It is exactly the same as I respond to all the other links during the whole year.
"We cannot talk every week about the players that are coming here to Manchester City and the players that are going out.
"He is a player of Manchester City, he is very happy here and the club is very happy with him also."
Pellegrini has also revealed his concern about the knee injury that continues to keep defender Matija Nastasic on the sidelines.
The Serbia international has missed the last eight games in all competitions having been out longer than initially expected.
Pellegrini said: "He continues with some pain in his knee. He has at least a couple more weeks to recover.
"Of course we are concerned because the doctor doesn't know what happened with him.
"He made all the exams that he needs but we don't know what happened with him.
"We are taking other opinions. The doctor is in charge of that.
"The player feels a pain inside the knee but nobody knows what the pain is."
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