De Bruyne has not played since late January, while Nasri's most recent game came last October when Bournemouth travelled to the Etihad Stadium.
"I'm not 100% sure but I think it will be difficult for Joe (Hart) or Yaya (Toure) to play against PSG," said Pellegrini.
"At this moment, Kevin and Samir are on the squad list. Maybe they won't play 90 minutes but they are ready.
"Kevin worked the whole week with no problem. Of course, it was a long time he couldn't play and the same with Samir Nasri. But I hope both of them will be important for the remainder of the season.
"Raheem Sterling has a muscle injury and will be out for four or five weeks, while Toure has a problem with his heel.
"At the end of the season, when you have so many players playing so many games, it's important to have fresh players coming in."