The Dutchman has been unable to find the form that made him such an appealing young player at Ajax.
Van de Beek, who left United for Girona in the summer, spoke about his several seasons of hell at Old Trafford.
He told The Athletic: “I think it was quite unlucky because I played some more games, especially closer to the winter, and then I got injured. That was not easy. It was very bad timing.
“If you start to play a little bit more, then you can get the rhythm of everything. But that injury arrived, you need to restart again, you need to come up. There are new players coming in, and you start from the backseat again. It’s difficult.
“I would say this was a key moment for me at Manchester United. In this period normally when you play, you get stronger and better. But I got this injury. That was tough.”