The Dutch winger failed to set the Premier League alight, despite arriving at United with much promise in 2015.
Signed by Louis Van Gaal, United fans felt they were getting one of the most talented youngsters on the planet in Depay. But he rarely impressed in the league and eventually moved on to Lyon, where he has excelled.
Simon Zwartkuis, who co-authored Depay's recent autobiography, spoke about the player's mindset and that failed stint at United in an exclusive interview with Tribal Football.
Zwartkuis said: "He [Depay] is very open about his time at United in the book. He had trouble adapting to the style of play under Van Gaal, where he experienced a lack of freedom on the pitch.
"While freedom to make his actions and follow his intuition makes him the specific player he is. After a while Van Gaal wanted him to work with a mental coach, but Memphis didn't know that person and refused. He thinks that was the start of the problems between him and Van Gaal.
"Also Memphis wanted to do extra training sessions with Ryan Giggs to become a better winger, but Van Gaal told him that was nonsense.
"Besides that Memphis admits in the book that during his first season at United he didn't reach his level he showed at PSV and the Dutch national team.
"When Mourinho came, the level of Memphis went up during training, his teammates asked him why he didn't get a chance in the starting line-up. But that never happened."
The author was also asked how Memphis looks back on his time in the Premier League with Manchester United.
Zwartkuis said: "He regrets that it didn't work out like everybody was hoping for.
"During that period he blamed Van Gaal and Mourinho for not giving him the trust he needed, but looking back in the book Memphis blames nobody but himself.
"He became more and more frustrated with his situation. Personally he hit rock bottom during that time, locking himself up in his house, not able to find his way up.
"At the same time he had discussions with his agent and mental coach about him driving to the club in his big cars and the problems that caused in the tabloids. All this aspects combined made it very difficult for him.
"Looking back Memphis tells that he learned a lot in England and the way things ended caused major changes in his personal and sporting life."
Zwartkuis even believes that Depay would consider a move back to the Premier League. After his time in France, he says as the attacker is a much better and more mature player and person.
He said: "Why not? He is a different person and player now, comparing to his time at United."