The 32-year-old is City's all-time leading scorer and the Etihad club will lose a substantial source of goals if he departs next summer.
Aguero has nevertheless missed much of City's campaign to date, having undergone surgery on a knee injury in June and suffered a setback upon his return last month.
The Argentine is being eased back into Guardiola's first team and the City manager said on Friday that he is prepared to be patient with Aguero when it comes to both his injury rehabilitation and his contract.
"He's going to give us a good moment this season. He is still not in his best condition. We cannot forget how long he was injured and come back and injured again," Guardiola said.
"In the middle of the season, he's a guy who needs to be so sharp but the quality to score in the box is always [there], always was and always will be.
"We don't have doubts about that. But he needs a little bit of time to get in the training sessions and the minutes. And after we have seven months ahead to show."
On his future, Guardiola - who recently extended his own stay at City for a further two years - said: "He's a guy who deserves with the club the fair talks to do what is the best for him for the club and for everyone.
"In that you should not doubt. As I said many times, I was lucky to play as a football player and manager with incredible football players.
"He's one of these ones, for sure. But especially as a human being. I never found a bigger star like him to be to be like Sergio is."
Aguero is grieving after the death of legendary Argentina player Diego Maradona, who is the grandfather of his son Benjamin. Aguero was married to Maradona's daughter Gianinna before their separation in 2012.
"It's difficult for me to talk about his feelings," Guardiola said. "I saw him good and of course the impact on the day of the game against Olympiakos was hard. Especially for his son.
"And, of course, it was was tough, it's normal. He knew Maradona quite well and he was the grandfather of his son. It's a sad situation unfortunately for his family and yeah, he's okay. But it's a question for him it's difficult for me to answer."