Aguero, 28, played for the last seven minutes in City's 2-1 win over Swansea on Sunday, when new signing Jesus opened the scoring and got a 92nd-minute decider.
"We are so delighted because most of the big important clubs in Europe want him and he chose to come here".
The 19-year-old Gabriel Jesus has started ahead of Aguero for Premier League games against West Ham and Swansea, and scored three goals.
Guardiola said "he will be so, so important".
Fernandinho said: "It was a very, very tough game for us, but Gabriel scored two goals and we were unlucky for theirs".
'In three years my contract is up, that's why I say I'm happy at the club. At the beginning of the season, few would have expected even Guardiola to leave a fully fit Aguero out for three matches running.
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Jesus' impact at City was expected by many, and Aguero's long-term injury record has made him vulnerable in Guardiola's plans.
The 19-year-old has changed the mood at City nearly by himself, and City have not lost since he made his debut against Tottenham Hotspur. As I say the club will decide if I have a place here or not.
Then there is the issue of his contract extension until 2020, signed at the beginning of previous year but mysteriously still unannounced more than 12 months later.
"I've played with Wayne Rooney and Michael Owen as teenagers and you knew straight away they had special talents".
Some scoffed when Manchester City swooped for Gabriel Jesus. Gabriel Jesus came to the rescue, though, tapping home a rebound from close range after his initial headed effort was only parried out by Swansea goalkeeper Lukasz Fabianski.
"I think he is angry and has desire and shows so many good things". "I am here and everyone in the club has helped me and try to help me get better every day".
And when Sigurdsson equalised with a low drive with less than 10 minutes to go, it looked like being another afternoon of disappointment for Pep, the groans growing ever louder as the game ticked into stoppage time.