The Argentine striker has long since cemented himself into legendary status at the Club thanks to his remarkable goal-scoring prowess.
To date, Kun has claimed an incredible 244 career goals for City – including 13 this season, despite the fact he has being sidelined for a number of weeks through injury.
Now back in contention after recovering from a thigh problem, Aguero could feature in Friday’s Premier League trip to face Wolves.
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And asked at his pre-match press conference ahead of the trip to Molineux on whether coping for life without Aguero in the future would be one of the Club’s biggest challenges, Guardiola was unequivocal in his response.
“It will be one of the toughest… I think Sergio is irreplaceable,” the City manager declared.
“We have an incredible striker in Gabriel (Jesus) and could maybe get another when Sergio is leaving but I think most important moment in this club, even more than if we hopefully one day win the Champions League, was the moment Sergio scored that goal against QPR.
“That was much better than four titles in one season and he was the guy.
“More than that the goals he has scored for this club. Sooner or later it will happen he will decide when and I’m sure the club will be ready to find the guy to replace Sergio but, of course, it will not be easy.”
Reflecting on his three and half seasons to date working with the Argentine, Guardiola was also effusive about Augero’s down-to-earth attitude and positive demeanour around the squad.
“I have never seen a big star like him be so humble, he’s such a funny guy,” the boss added.
“It’s a joy to work with him and how he accepts my decisions even when it has not worked for him. Big stars like him cannot accept that sometimes.
“I have worked with some other stars who think they are more of a star than Sergio and they were not and they more difficult to handle
“It’s not easy to find a guy with his status, personality, what he has done in his career, his humility.”
Pressed more on Aguero’s remarkable career, Guardiola also said he was in no doubt that the 31-year-old more than merited his pace amongst the best all-round goal-scorers he had ever seen and worked with.
“Well in the box he is incredible, but I was with some other guys who were not bad!,” Pep added.
“I remember Ronaldo (the Brazilian forward), I remember Romario, I remember Et’o - he was one of the most incredible strikers I saw in my life, he could do everything - and Sergio is there too.
“OK, Messi is a little higher but Sergio is up there.”