While Mainoo is only 19, he is already one who looks assured in the Premier League.
"Obviously, I was on loan for a few seasons and came back that pre-season (2022) and saw him in training," Bernard, now of Sheffield Wednesday, told the Manchester Evening News.
"I was thinking: 'Who is this kid?' You could see straight away from the stuff he was doing in training that he was going to be a top, top player.
"His dribbling was remarkable, going through players easily, just striding like he wasn't even trying. You could see straight away that he was one of those special players coming through the ranks and I am proud to see him playing for United and doing what he is doing. He deserves it.
"He is one of them kids that doesn't really talk too much, he was a bit shy (coming into the first-team). He just let his feet do the talking and you can see that even until now. He is a special talent.
"His mindset to the game is like someone who has been playing for years; he is just that type of professional. He is someone who just gets his head down, works hard, does what he's told. He's willing to learn, he's willing to work hard for the team and I think that is what United need.
"They need people who are willing to get their heads down, work hard, run about and give energy. I am really happy to see what he is doing."