Toure, a midfield talisman at the Etihad Stadium since his signing from Barcelona in 2010, has performed below his usual high standards for much of the current season.
He was sent off for an act of petulance in the midweek Champions League loss to CSKA Moscow and there have been reports that City are now willing to consider offloading him.
Paris St Germain have been linked with the Ivory Coast international but Pellegrini is adamant the 31-year-old will be staying.
Pellegrini said: "There must be a lot of reports telling (the story) that Yaya will be sold
Maybe (it is) all the other teams that want Manchester City to be a weaker team.
"Yaya is a very important player
He played very well in the first half (against CSKA) - he scored a goal
In the second half he made a mistake and he was sent off but - never in my mind - I am sure nobody at the club is talking about selling Yaya Toure.
"Maybe that news comes from other teams (who want) to see our team weaker."
Toure was outstanding as City won the Barclays Premier League last season, scoring 20 goals in the competition.
Problems began in the summer, however, as he voiced criticisms of the club and then became embroiled in a row over how his birthday was celebrated.
There was also tragedy as his brother Ibrahim lost his battle with cancer and earlier this week he was the victim of racial abuse after reactivating his Twitter account.
His form on the pitch is part-reflected in City's underwhelming start to the season
City are yet to hit their stride in the Premier League and are facing early elimination from the Champions League.
Last Sunday's derby victory over Manchester United was City's only win in five games.
As well as players' performances being questioned, Pellegrini is also starting to find himself in the firing line, but the former Real Madrid coach has again insisted he does not feel pressure.
The Chilean said: "I never feel pressure
In my career I have had 25 years managing teams and the only pressure I feel is my own pressure to return to play in the way I like this team to play, to play attractive football and be a winning team.
"I don't read press, I don't have any other pressures
I don't feel external pressure (and have not done) in my whole career."
Pellegrini insists it is too early to be writing off his side
They trail leaders Chelsea by six points in the Premier League but are still third
At the equivalent stage last season City were fifth, trailing then leaders Arsenal by six points.
The Champions League challenge is more precarious, with just two points gained from four group games but City could yet progress if they can hit form against Bayern Munich and Roma.
Pellegrini said: "It is difficult to progress in the Premier League when you won the title last year but we try to continue fighting for the title.
"I don't know if you can take some conclusions when you have to play 28 games more
It is a lot of games and we are just in November.
"About the Champions League, we have to take the conclusions when we have finished the group
If we don't qualify it will be a step back but you can't talk about things you don't know will happen.
"I always say that mathematics can give you qualification and we are going to fight for it
We have six more points to play for."
Pellegrini is hoping for a reaction as City travel to QPR, although weakened by the absence of injured captain Vincent Kompany, on Saturday.
He said: "Yes of course, I want to see the same team we saw in the derby three days before.
"It is very important to return to the Premier League, trying to continue winning so we can fight for the title until the end.
"In this moment we turn the page because it is very important to continue in Premier League the way we are doing now
We have won four of five games that we played in the Premier League.
"It is difficult to recover physically and mentally in less than 72 hours from what happened on Wednesday but we are trying to do it and I hope tomorrow the team that start will have the answer for the moment."
Source : PA
Source: PA