The American goalkeeper has been out since our win against Brentford earlier this month with a shoulder problem.
And speaking at his pre-match press conference ahead of the trip to the Weston Homes Stadium, the boss confirmed he would still unavailable for the trip to face the Championship with the boss taking a decision on who will play in goal tomorrow.
Asked if anyone would be missing, Guardiola said: “No. Some knocks, but today everyone trained.
“Zack Steffen - Not yet (will he be back).
He has a problem with his shoulder and as a goalkeeper it is difficult. He is still in the gym.
“(We will) Decide tomorrow with Xabi (goalkeeper coach Mancisidor) (on who will play in goal). Tomorrow we’ll talk about that.”
Looking ahead to the match, the boss also confirmed that Ukrainian international Oleks Zinchenko would play.
And Guardiola said that he felt playing his part in the Club’s quest for success would be positive for Zinchenko in light of the current situation in his homeland.
“Yeah, Absolutely (he is fine),” Guardiola added.
“I think it will be good for him and to show that the reason why he is here is because he is a magnificent player.”
Looking ahead to the game, the City boss said he was expecting a tough test from the Posh, despite their current travails in the Championship.
While City lead the way by six points at the top of the Premier League, Peterborough lie bottom of the Championship.
But he said the opportunity to tackle City would provide a completely different incentive for the hosts.
“It is one game, it is a final,” Guardiola added.
“Of course, they are not in the best position in the Championship
“We prepare well, we prepare well today and tomorrow to go and try to get through to the quarter-finals.”