And Advocaat - who handed him his debut at PSV Eindhoven - believes the winger may need to look elsewhere for first-team football.
"The potential is there for him to be a good player," Advocaat said. "You cannot lose that, he has the quality to be a top player, but the problem for him is that there are so many quality players in that squad.
"So for himself it is important to start playing regularly at the age that he is at - otherwise the way, I think, is that maybe he has to find another solution [club] because he is too good to sit on the bench. I still believe in him, he has the right mentality, the right character to play for United, but there are so many options there. Regular playing time will help his progression."