Nasri is returning from a calf injury and could take his place on the bench after training with the first team squad for the last two days.
Mangala, meanwhile, has picked up a shoulder problem and will be checked before the game.
The Blues are five points behind Chelsea but Pellegrini denied the Stamford Bridge battle would be key to the title race.
He said: “I think it’s a very important game, but not the game to decide the title because after that we have 45 points more.
“If you remember this group won the title after being eight points behind Manchester United. In football you never know but it’s an important game to close that gap as soon as we can.”
City go into the game without midfielder Yaya Toure, who is with Ivory Coast at the African Cup of Nations.
Pellegrini was quick to point out that his squad are capable of producing results without Toure and that any top squad must be able to cope without star players.
“It is up to other players to demonstrate what they can do,” he reflected.
“Yaya is a very important player for us but it would have been difficult for him to return from the African Cup of Nations after just two days had Ivory Coast been eliminated.
“We played without Yaya in Rome and qualified and we also beat Bayern Munich in the Champions League without him.
“So he is a very important player. The same can be said of Diego Costa but I don’t think either team depends on just those players.”
Costa will miss the game after being retrospectively banned by the FA for stamping during Chelsea’s midweek Capital One Cup victory over Liverpool.
Pellegrini added: “Costa is a great player. A very important player. He has his character and I hope this punishment will be a good thing for him for the future.”
