Pep Guardiola suggested Manchester City might have been fighting for the title rather than scrapping for a Champions League place had "special" Gabriel Jesus been available all season.
Jesus, 19, did not complete his move from Brazilian club Palmeiras until January and after scoring three goals in his first three starts, he was struck down by a broken foot in mid-February.
He made a lively return in Thursday's 0-0 draw with Manchester United, seeing a stoppage-time header ruled out for offside, but has rejoined a top-four chase rather than a Premier League title challenge.
"We saw after three months out, in five minutes he created two chances and one goal (that) for centimetres was not a goal," said Guardiola, the City manager.
"He has his instinct. Next season he will be there with us. I always have that thing in my mind, 'What would have happened if we'd had Gabriel Jesus all season?'
"We didn't buy another striker because we bought him, but he could not come before January, which means September, October, November, December, four months without him.
"When he arrived, his impact was instant. It was so great in a tough league like here. But he could just play three weeks.
"I don't know what could happen with him and Sergio (Aguero) playing a lot of games, especially games here (the Etihad Stadium) where the defences are so, so deep.
"I will never know. I would like to know what would have happened in many games when we missed those chances because he has this instinct in the box."
- 'We cannot miss' -
Despite the Brazilian forward's tender years, Guardiola says his work ethic makes him an example to his more experienced team-mates.
"He's dynamic, he's aggressive. For the midfield players, you look at how he goes to press, how he attacks the box," said the former Barcelona and Bayern Munich coach.
"His influence on his team-mates is huge, amazing. But now we are so happy that he's back. He couldn't play more minutes because he's just had two training sessions after three months (out).
"But he's physically strong and I'm pretty sure he's going to help us until the end of the season.
"You cannot compete all the season with big teams like Chelsea and Tottenham and Liverpool and big teams in Europe without a squad with big players.
"Of course Gabriel is a number nine from Brazil. Everybody notices how good he is, how special he is."
Thursday's stalemate with United enabled City to preserve their grip on the Premier League's fourth and final Champions League qualifying slot.
Guardiola said he did not yet know whether Jesus will be able to start Sunday's game at second-bottom Middlesbrough.
City lost a sapping FA Cup semi-final against Arsenal after extra time last weekend, but with United and Arsenal snapping at their heels in the league, there will be no let-up in the weeks ahead.
"We had a tough, tough game in our semi-final against Arsenal at Wembley," Guardiola said.
"We recovered quite well. The previous two days, people were dead, tired. (Against United) we showed how mentally strong they are.
"But now we have just two and a half days, we travel to Middlesbrough. So we have to analyse exactly what the people need, because of course now we cannot miss.
"If we miss one shot, we will be out of the Champions League next season."