McDonald joined the Iron on loan but suffered a back injury in his first training session, meaning he has yet to make his debut.
He returned to Lancashire for training, but is now back in North Lincolnshire.
United have several injury doubts for Saturday's trip over the Humber Bridge to take on Hull.
David Mirfin is a serious doubt with the foot injury he suffered during Saturday's loss to Leeds, while Martyn Woolford (groin) and Sam Togwell (leg) missed traniing on Monday.
There is better news for Joe Murphy, with the Iron's first-choice goalkeeper expected to return at the KC Stadium having missed the last two games with a groin problem.
Source: PA