McCombe is highly rated at the club, and recently was rated as one of the top ten prospects outside the Premiership in the Observer Sport Monthly.
The six foot six inch has been attracting the interest of a host of Premiership clubs, with Tottenham Hotpsur the latest club tipped to make a move.
United would be reluctant to let their star prospect leave Glanford Park, but any bid over £500K from Glenn Hoddle would almost certainly see the youngster move down south.