The 22-year-old made just one United start since Mourinho replaced Louis van Gaal in the summer and joined Lyon in a deal worth around €25 million (£21.7m) in January.
However, the Dutchman insists he has no bad feelings towards his former coach.
“I have no bitterness towards Mourinho,” he told beIN Sport. “I did what I had to do in training. Of course, I didn’t understand his choices, but he was the boss. I had to accept those choices. I think I was not good enough for him. But it’s okay, I’m showing my quality here.
“I’ll be back to the top and we’ll see what will happen.
“Leaving Manchester United? That was not complicated. I’m young, I need to play.
“When I think about the last time I played a whole 90 minutes before coming here, it was a year ago. It’s incredible.”
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