Jesus had an immediate impact after making his City debut as a substitute against Tottenham in January, scoring three goals in four Premier League games and forcing Sergio Aguero out of the team.
But the 20-year-old broke a bone in his foot in mid-February, rehabilitating on the sidelines until this week when he returned to training with the first team squad.
Guardiola has not ruled him out of starting in Sunday's Wembley semi-final, although he is more likely to be on the bench, but the City manager still expects his new start to have an impact on the rest of the campaign.
"He has made an impact. You know how difficult it is to come into the Premier League and play how we play," Guardiola told reporters on Friday.
"In just 10 minutes against Tottenham he created two or three chances himself and scored (a disallowed goal). He has an impact for sure.
"In any case when players are injured, I am happy they are coming back, especially for him. He decides, he has all Europe in his hands, and he decided to come here and join us. We can't forget that.
"I am so happy he joined us here but then he could only play two or three weeks so that is why I am so happy.
"With Sergio and the other ones he will hopefully help us score goals until the end of the season."
England defender John Stones is out of the semi-final, although he is expected to recover from a muscular injury in time for Thursday's Manchester derby against United.
But all eyes will be on Jesus and what role he may play, with Guardiola taking a decision after the team has travelled to London.
- Silverware collection -
"No," said Guardiola when asked if he had ruled Jesus out of starting.
"He's really much better. Today he will take part in training with us. He's coming back with his happiness and we are so happy he's back again.
"We are going to travel with all the squad to Wembley, all the group, and he will be part of that. After that, we will see.
"All the squad are travelling down tomorrow and we will watch the match between Tottenham and Chelsea. After dinner I will decide the team."
The FA Cup remains Guardiola's only hope of ending his first season in English football with silverware to add to his considerable collection and he admits that the club's owners may not be satisfied if he fails to win the competition.
"I think they will not be happy," Guardiola said. "The expectation of the club is as high as possible, winning titles. And we are not able. We are not happy, I can completely understand.
"And we could have done better in terms of the results and even in the way we played because we wanted to be in the race for the title and in the Champions League until the end.
"Despite the fact that I am happy with what we've done, it is still not enough.
"But they have to decide. They are my bosses. The chairman and the owner have to decide whatever they want. But you are here asking every few days asking my opinion and I am honest.
"Because I'm a guy who if we don't play well I say we don't play well.
"And when I said about the circumstances where we have come from in the last two seasons, the way we played we have made some good things."