The City playmaker has struggled with an ankle injury picked up during the World Cup and has also had limited opportunities due to the form of wingers Jack Grealish and Riyad Mahrez.
But his boss is backing him to find his best form and force his way back into the starting XI sooner rather than later.
“He struggled with his ankle after World Cup – and a lot.
“He made an incredible effort playing with pain. Arrive in the moment, he said to me ‘Pep, I cannot (continue) anymore so I have to rest and have to recover.’
“And we gave him, long time ago, one or two weeks off to not play and after that Riyad was in his best moment of the season and Jack made a step forward.
“If you intend to say I don’t trust Phil, forget about it. Phil is our diamond.”
Guardiola said it is down to Foden to now challenge his in-form team-mates and win his place back.
“I want Phil to push them and of course Phil can play in the middle, in a position more central,” he said.
“It’s not about lack of confidence or whatever. I thought a lot to put Phil in last 20 minutes to make his impact.
“And always in the past, always he did. In this season, a little bit less when he came from the bench.
“Phil always has, since I arrived, when he was 17, 18, 19-years-old, he played five minutes, and it was the best five minutes of the team.
“This season it was not like that. I think he struggled with the ankle in that position. I was thinking a lot to put him (on against RB Leipzig) but in the moment I felt the team came back to what we had in the first half.
“And that’s why I didn’t want to change it. That was the reason why. Of course, the people will not understand it.
“So, at the end, the people or the referee say (it was handball), you know, in the last minute (versus Leipzig) - oh sorry, because it was not hands…
“Anyway, just in case it was handball, (we would have) won the game and no substitutions was a good decision.
“Some players, after World Cup, struggle a little bit. The other ones, no.
“There are players who struggle a little bit. I think Phil as well apart from the physical situation.
“But here comes the best part of the season.
“Always I said to him that the best part is here, you are so young, next season is a new one.
“You drop a little bit this season comparing the previous ones, it is absolutely a normal process.
“So how you handle it? This is the question.
“You handle good, still training as an animal. There is no doubt about it. He will be back.”