Thomas Tuchel once again left the 26-year-old out of his squad for the upcoming Nations League fixtures, despite Foden having recently shown signs of rediscovering his best form at club level.
The midfielder has been left out of England's plans again, but Maresca was surprised by the decision when asked about it at Friday's press conference ahead of City's Premier League trip to Nottingham Forest.
“He is doing well. I don't know why he has been left out of the national team, but we are happy with Phil,” the City manager said.
Maresca acknowledged that Foden still has more to offer, but stressed that his responsibility is to help the midfielder gradually return to the level that previously made him one of the leading players in English football.
“We know that he can give much more, we know that. But slowly, slowly, it is my duty to help him. He will be back and be one of the best,” he added.
Foden has recently contributed to Manchester City's improved attacking form, including a hat-trick in the Champions League victory over AEK Athens. He will now remain with his club rather than join England for the matches against Croatia and Spain.
### Maresca also backs Donnarumma after errors
The manager was also asked about Gianluigi Donnarumma, whose recent mistakes have attracted scrutiny following errors against Paris Saint-Germain, Aston Villa and RB Leipzig.
Maresca refused to make the goalkeeper's form a major concern, pointing instead to the saves he has produced and the Italian's own awareness of his mistakes.
“He's good, overall he's good,” Maresca said of Donnarumma's mood. “He's quite relaxed, in terms of recognising that he has made some mistakes but has made some good saves.”
The City manager said he had spoken to the goalkeeper but did not feel the need to go into extensive detail because Donnarumma already understood where he had gone wrong.
“He recognises that he has made some mistakes, but at the same time recognises that he has made some great saves,” Maresca added.
Donnarumma was beaten at his near post during Wednesday's Champions League match against Leipzig, but Maresca pointed out that the goalkeeper had also produced an important stop earlier in the game.
City travel to Nottingham Forest on Saturday, with Maresca backing both Foden and Donnarumma to respond positively as the club enter the final fixture before the international break.