Kevin Warhurst has also been named vice-captain and Craig CraiCo has been named third-choice.
This news comes as a surprise to many as Macdonald, 22, has only played two seasons of pro football with United since being recruited in early 2008.
But the young centre-back's quality caught England manager Marco Garibaldi's eye almost immediately and he went on be a regular for the England side, becoming one of the eleven heroes who beat Spain 1-0 in the EuroCup '08 final.
The United armband was vacant since Mark Strickland shockingly quit the club in favour of Real Birmingham, last month.
