The 20-year-old had been sidelined after picking up an ankle injury in pre-season, but Pellegrini has confirmed that he will be ready to face Hull City at the Etihad on Saturday.
"Matija is available to play. I think Javi Garcia didn't do a bad job as he normally plays in midfield but it is Nastasic's natural position, so of course it is better we have him there," Pellegrini told reporters at a press conference.
"Nothing is new with Vincent [Kompany's injury]. [At the time] the doctor said it will be four to six weeks. Maybe next week we will see how he improves but less than one month is impossible. Micah [Richards] is not available for this game but I hope that next Monday we will start working normally with him."
City have taken three points from their first two league games.