The Argentinian is now feeling better after a bout of coronavirus but has not yet been given the all-clear to return to training.
“Sergio is not yet here,” Guardiola said at a press conference. “When he tests negative he will come back. We still don’t have the results yet.”
Aguero, who has started just three games this season, is unavailable for Saturday’s Premier League clash with Sheffield United, a match that even without one of their star men, City remain the sports betting favourites for a convincing win.
Defender Nathan Ake is also still out through injury.
Guardiola said: “(He is) not yet available. It is the same guys (available) that were in the last games.”
Guardiola was unwilling to discuss the future of defender Eric Garcia, who is in the final year of his contract and has been frequently linked with a return to his boyhood club Barcelona.
He said: “I don’t want to say anything about this case. He’s our player, the transfer window finishes in a few days.
“He is fully committed while he is here. He is an exceptional player and guy and that’s all.”
City host a Blades side on Saturday that, despite being bottom of the table, pulled off a shock win over high-flying Manchester United in midweek.
That result allowed City to retain top spot in the table heading into this weekend’s fixtures.
Guardiola said: “Of what I saw before the United game, Sheffield (United) is a team that is alive from their body language.
“It is not easy with the results they have got this season and that speaks incredibly well about (manager) Chris (Wilder), his staff and the players.
“The result against United speaks for itself. Everybody knows how difficult it is to win at Old Trafford.”