The Premier League champions are looking to trim their squad before the close of the transfer window.
Goal UK reported in July that Nastasic has attracted interest from Roma, Inter and Fiorentina and Pellegrini says that the Premier League champion has received offers for the 21-year-old, who is now considered the club's fifth-choice center back.
"Matija needs to play. We already have important players here with four fullbacks, [Martin] Demichelis, [Vincent] Kompany, [Eliaquim] Mangala and [Dedryck] Boyata," Pellegrini told the press. "So we will see in the next few days what happens with Nastasic. He is an important player but he has offers and I think the best thing for him is to play.
"That also goes for Micah Richards, who didn't want to continue here because he wants to play more — he had a contract to renew but didn't want it."
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Richards is desperate to leave City, with one year remaining on his contract, and is expecting the Premier League champion to lower its 8.75 million euro asking price, with Liverpool, Tottenham, Everton and Newcastle having shown interest this summer.
Guidetti, meanwhile, spent the second half of last season on loan at Stoke City, but Feyenoord coach Fred Rutten says the Dutch club is keen on a move.
"So we have three or four players extra — Scott Sinclair and John Guidetti are also important players, but I don't like to have so many in the squad," Pellegrini said. "I think 22 players is enough and they are all players who have a lot of quality. It is good for them to play."