Feyenoord boss Ronald Koeman, who will leave the Rotterdam club this summer, has already advised De Vrij and Martins Indi to consider quitting the club also to make progress.
“It is clear that players are ready for a step-up after a few seasons at Feyenoord,” he said.
“You’ll end up better off, but then you have to make the right choice.”
New United boss-elect Van Gaal is a keen advocate of bringing young players through and the threesome are ready to test themselves away from the Dutch Eredivisie.
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