The Frenchman was criticised by former boss Roberto Mancini last season, after a string of indifferent performances.
He starred in City's recent derby win, and Pellegrini believes that he will be a key player throughout the season.
"I don't talk about what happened in the past but at this moment Nasri is playing very well," Pellegrini told reporters.
"I talk often with him because I know how much he can do as a big player. He knows he must play the way I know he can. If he doesn't maybe we have other choices but Nasri is absolutely committed with the team and with me.
"We hope we will see a great Nasri the whole year."
City face a trip to Aston Villa this afternoon.