The Brazilian goalkeeper was withdrawn as a precaution at half-time in the San Siro, where City drew 1-1 and finished with Kyle Walker in goal after substitute stopper Claudio Bravo was sent off.
Guardiola was delighted with the right-back’s contribution between the sticks and revealed he was chosen due to his speed and bravery.
“I don’t know right now,” he said when asked the extent of Ederson’s injury.
“It’s a muscular problem. It was a risk so we took him off as he was feeling it late in the first half. We don’t know.
“For the last 15 minutes we had a situation with the new goalkeeper we have at the Club and it was difficult.
“Kyle was suggested because of his courage and he’s quick. Congratulations to him for helping the team and going in this position.”
The remarkable turn of events made for a nervous final 10 minutes for City, who, after taking an early lead through Raheem Sterling, dominated the first half but saw Gabriel Jesus miss a penalty that proved costly.
The hosts were much improved after the break and forced a leveller through Mario Pasalic as City, by comparison to our fine first half showing, toiled somewhat.
Guardiola admitted the level of performance dropped in the second period, but he had no complaints with the result and was satisfied with a point that maintains our unbeaten record in the Champions League and keeps us on track to reach the knockout stage of the competition.
“We did really well in the first half where we were outstanding, but with the problems we had in the second half, we suffered," he added.
“The second half we didn’t do what we did in the first half because we didn’t play the way we wanted to, but it is normal and it happens in football.
“We conceded to the top scorers in the Italian league who create a lot of chances. You’ve got to take your hat off to Atalanta. We see them play week in week out, we know how good they are.
“It is a good result away against a good side and we need one more point to win the group and hopefully against Shakhtar Donetsk at home we can do that.”