The 22-year-old was linked with Liverpool and Tottenham in January, back when he was still with Utrecht, but the interest was ended when it was apparent that van Wolfswinkel required surgery to treat a collarbone injury and would be out for the long term.
Van Wolfswinkel instead joined Sporting from over the summer for €5.4million, and has been in a rich vein of form, scoring six goals in his last six appearances, including a cheeky backheel against Lazio in the Europa League.
The achievement has not gone unnoticed and has reignited rumours of interest from England, although the speculation comes from Premier League holders Manchester United this time.
Phelan revealed that United have been long-term admirers of the young Dutchman.
"We have obviously known Van Wolfswinkel for a long time," he told Record. "He is a young striker, very talented, who has been growing in the last few seasons.
"A club like Manchester United carefully follow many players all over the world."