Aguero has sat out the last two games with a muscle problem and will also miss the Champions League clash with Olympiakos at the Etihad Stadium on Tuesday.
The 32-year-old is nearing a return to training but Guardiola will not risk a setback if he is not fully fit for Liverpool's visit on Sunday.
"We don't want to make a step back again but he's getting better," Guardiola said at a news conference on Monday.
"He's getting better. I don't know about Liverpool but after the international break for sure he'll be ready."
Gabriel Jesus is also close to a return after rejoining training on Sunday. The Brazil international has not featured since City's first game of the season. However, the Olympiakos game could too soon which raises the possibility that Ferran Torres could be again used a makeshift centre-forward.
"It's too early to know, we'll see at the last training," Guardiola said.
"He did one with the team [on Sunday]. We'll see. We're happy he's back. We're awaiting Sergio but we've been happy with Ferran so we have an alternative."
Meanwhile, defender Nathan Ake has urged Guardiola to extend his stay at the club.
"I think the manager has been so good for this club," Ake said. "That is also one of the reasons I joined so it will be good. Obviously it is up to him. We focus on this season and he is trying to win titles. We focus on that first and who knows what comes after."