The striker has a contract at the Etihad Stadium until the end of the season and could leave the club for free in the summer if fresh terms are not agreed.
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Guardiola has backed Aguero to get back to his best after returning from injury and said the 32-year-old will be given the right to decide whether or not to extend his contract.
"He is a guy who deserves with the club, fair talks to do what is the best for him, for the club and for everyone," Guardiola told a news conference on Friday.
"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 is one of these ones, for sure. But especially as a human being. I never found a bigger star like him to be like Sergio is.
"He is 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.
"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, always was and always will be. We don't have doubts about that."
Guardiola will have a fully fit squad to choose from for the first time this season when Burnley visit the Etihad Stadium on Saturday.
"It's difficult for me to talk about his feelings," Guardiola added. "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 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."