McCormack’s action was taken a day after the unveiling of Dave Hockaday as the new head coach at United, but his decision is not thought to be directly related to the former Forest Green manager’s appointment.
The 27-year-old’s departure from the club has looked inevitable since it was announced that he did not travelled out to northern Italy for United’s two-week training camp in Santa Cristini.
The Scottish international is the subject of considerable interest from Fulham, who are hoping to finalise a deal to take him to Craven Cottage shortly.
Fulham saw a £5m bid for the Scot turned down last month, but have maintained their interest in the forward, who has also been linked with moves to West Ham and Newcastle United this calendar year.
McCormack signed a new four-year deal at United last autumn, but has grown disillusioned with events at Elland Road and held a face-to-face meeting with owner Massimo Cellino expressing his concerns recently, with reports suggesting he had asked to leave.
Fresh reports this morning say he had tabled a transfer request, although the club have not confirmed the development.