Earlier on Monday, it was reported that the Red Devils had made an approach to the Championship counterparts for the 52-year-old, who previously spent a decade on the books at Manchester City.
However, Southampton immediately rebuffed the proposal and were apparently irritated by the timing of Man United's enquiry just before their crucial league clash with fellow promotion chasers Ipswich Town.
The Saints ended up suffering an excruciating 3-2 loss to the Tractor Boys thanks to Jeremy Sarmiento's dramatic injury-time strike, leaving them 12 points off the automatic promotion places with two games in hand.
Southampton are said to have turned down a compensation package worth a full year of Wilcox's salary from Man United, who were not prepared to go higher and insisted that the correct protocol had been followed.
Sir Jim Ratcliffe on verge of latest high-profile appointmentHowever, the Red Devils need not worry about negotiating a fee with Southampton, as according to Fabrizio Romano, Wilcox has now handed in his resignation and is set to head to Old Trafford.
The 53-year-old will supposedly act as Man United's technical director under Sir Jim Ratcliffe, and he quickly decided that he wanted to join the 20-time English champions after hearing of their interest.
As Southampton rejected Man United's financial proposal, Wilcox took matters into his own hands, and the former England international is now understood to have agreed his contract with the Premier League side.
Wilcox's return to Manchester will see him reunite with Omar Berrada, whom he forged a successful relationship
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