Donnarumma, widely considered the world’s best keeper, joined City from Paris Saint-Germain on deadline day, while Ederson departed for Fenerbahce.
Guardiola also praised Erling Haaland, asserting he would not swap the prolific Norwegian striker for any other player, including Alexander Isak.
City faces Manchester United in a derby match on Sunday, aiming to improve their form after two recent defeats.
Forward Omar Marmoush is expected to be out for several weeks with a knee injury, and defender John Stones is a doubt for the derby due to a muscular problem.