Manchester United manager Erik ten Hag gave the 18-year-old 72 minutes, helping the visitors lead 2-0 over the weekend.
Mainoo – who was born in Stockport – has represented England at junior level up to the Under-19s but he is also eligible to play for Ghana.
That has led to fears the starlet could choose to switch.
However, according to the Daily Mail, FA chiefs are confident Mainoo will stick with England.
The midfielder has been a regular at St George’s Park in recent years and has staff convinced he wants an international career with the Three Lions.
It is claimed Mainoo has impressed coaches at England’s training facility with both his ability and work ethic. And he has been tipped to one day rival Declan Rice, Jude Bellingham and Kalvin Phillips to a place in Gareth Southgate’s midfield.
Lee Carsley’s England U21s are not in action again until March, when they face Azerbaijan and Luxembourg.
Mainoo is expected to be in contention for a place in the squad should he continue to feature regularly for United’s first-team. The starlet was given a glowing review from Ten Hag following the victory at Goodison Park. He said: “He has a lot of abilities and it was a really disappointing moment in pre-season when he got so badly injured.
“For him but also for our team, because I know he can progress a lot if he plays many of such games as today. “I know young players will develop very quickly and we thought it was the moment to bring him in. “We prepared him properly but he did a great job and now he has to build on this.”