The France centre-back joined City from Porto last month, for a reported fee of £32 million.
However, the former Standard Liege man has yet to make his debut for his new employers after being given an extended rest to help him recover from his exertions in the World Cup with France.
Captain Vincent Kompany and Martin Demichelis have anchored City's defence in Premier League games against Newcastle United, Liverpool and Stoke City.
Pellegrini insists Mangala will get his chance, but says the 23-year-old will need to produce consistent displays.
"We need the three of them [Kompany, Demichelis and Mangala]," Pellegrini said.
"Like I have said about the strikers, it's the same with the defenders.
"We have so many games to play. At the moment Demichelis and Kompany are playing well, but that doesn't mean Mangala can't play.
"He will have his time to play, and then it depends on performances."
