Foden scored 28 goals for club and country in all competitions and was named PFA Player of the Year but has begun four of his five games this time on the bench with his only start coming against Watford in the League Cup.
Speaking ahead of City's Champions League clash away in Slovakia against Slovan Bratislava, Guardiola said he was not concerned, saying Foden is getting back up to speed.
"Maybe I can have some doubts in many things, but Phil Foden is going to be back! As much as he feels good, he will be back," Guardiola told reporters.
"I think in 30 minutes at St James' Park (against Newcastle on Saturday), I felt already something that I like that I didn't see for example against Watford."
Foden is yet to score this season but an away trip to Bratislava, beaten 5-1 in their opening game at Celtic, could be the moment for him to open his account.
"Don't forget after the Euros he didn't have any training for two months, he had problems with some niggles and some problems in his health," Guardiola said.
"But now he is smiling and he's in his rhythm. He was the best player in the Premier League last season so we need him, he was important for us, but I have no doubts with his love for football and his training and passion, he will be back."
City drew their opening Champions League group game 0-0 at home to Inter and will be expected to dispatch Slovan Bratislava on Tuesday with ease.
"I have incredible respect for all the teams in the Champions League especially when you play away," Guardiola said. "Hopefully we can be aggressive and take the result that we need.
"I have learned (in my career) that nothing is for granted. Nothing comes for free."
It was a theme continued by City defender John Stones who was part of the England team that came within seconds of losing to Slovakia in the last 16 of EURO 2024 in June before going on to win 2-1 and go all the way to the final.
"We know the quality that they've got. That game went right to the wire, they made it so difficult and we know that tomorrow night they will be well organised and it will be an incredible atmosphere," Stones said.
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