The Dutch winger, 25, spent 18 months at Old Trafford before being shipped off to Lyon in 2017.
The forward has now opened up over his harrowing experience at the Theatre of Dreams.
Writing in his autobiography 'Heart of a Lion', Depay blasted: “I was convinced I could add something that wasn't there yet. Creativity. Boldness. Moves.
“Manchester United is one of the biggest clubs in the world. In name.
"But for years, they played football that put you to sleep."