Van Stijn has questioned whether the former Ajax midfielder's game suits United's style.
He told De Telegraaf: "He now has to play football in a way that he has never done before.
"The securities have disappeared. In the Ajax system, the running lines for these type of midfielders are completely different. At Manchester United he makes the same runs, but very often for nothing, because those balls do not come.
“So when they end up in a completely different environment, they are thrown far back, because they suddenly have to do things that they have not learned.
"(Davy) Klaassen managed to get through this at one point at Werder Bremen, but it is not an easy process."
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