Pep Guardiola would love to know how Manchester City's season might have turned out with a fully fit Gabriel Jesus. 

City is fighting solely for UEFA Champions League qualification, distant from the Premier League title race and coming to terms with last weekend's 2-1 extra-time defeat against Arsenal in the FA Cup semi-finals.

Jesus made an instant impact when he arrived from Palmeiras in January, scoring three times in his first two Premier League starts, but the Brazil striker then suffered a broken metatarsal at Bournemouth in February.

The 20-year-old frontman made his return as a late substitute during Friday's (AEST) goalless derby against Manchester United at Etihad Stadium, where he immediately unsettled the massed ranks of United defenders, had a goal ruled out for offside and left boss Guardiola pondering what might have been.

"We saw his impact after three months out, in five minutes he created two chances and one goal that, for a centimetre, is not a goal," the former Barcelona and Bayern Munich coach, who will end a season without a trophy for the first time in his managerial career, said.

"So he has this instinct. Next season he will be there with us. When he arrived his impact was instant in a tough league like here, it was so great but he could play just three weeks."

Sergio Aguero scored 12 goals in as many games during Jesus's time on the sidelines and has moved on to 30 for the season.

Jesus's breakthrough briefly left Aguero on the bench and speculation over his future at City and suitability for Guardiola's style have persisted.

But the Catalan suggested pairing the frontmen together could have helped to improve a disappointing return of eight wins from 16 home matches overall in the top flight.

"I don't know what would have happened in a lot of games with him and Sergio, especially in games here when the defences are so, so deep," he said.

"I will never know. I would like to know what would have happened in many games when we missed these chances because he has this instinct in the box.

"He's dynamic, he's aggressive. The midfield players, the second line, can just look at him to know how to go to the press, how to attack the box. His influence on his other team-mates is huge, it's amazing.

"Gabriel is a number nine from Brazil. Everybody notices how good, how special he is and hopefully next season, when the team is going to try to get better, he is going to help us more."

Guardiola, whose side travels to Middlesbrough on Monday (AEST) lying fourth with a game in hand on third-placed Liverpool, was keen to stress he remains satisfied with the efforts of Aguero, Leroy Sane and Raheem Sterling in attack despite bemoaning the absence of Jesus's cutting edge.

"The other guys have made a lot. Leroy in the last two or three months was outstanding," he added. "Before the United game, Sergio scored in the last 12 games one goal a game.

"His numbers are there, he has scored a lot of goals. I would like to see him with another guy helping him, to take a lot of pressure in that sense.

"Of course [Sterling] has room to improve. If he doesn't believe that he will make a huge mistake. His season has been more than good. He has created a lot of chances, scored goals, assists, and won penalties."