McDonald has consulted a specialist over his fight for fitness after hernia surgery.
The former Celtic frontman arrived on Teesside last month having already had his operation but has struggled to shake off the after-effects.
However, New Zealand international Chris Killen is expected to return to the squad against Rangers after recovering from the hamstring problem and virus which have kept him out of the last three games.
Rhys Williams (pelvic injury) and Chris Riggott (hamstring) are back in training but defender Tony McMahon is out with a stress fracture of the foot.
Long-term absentees Seb Hines (ankle and medial ligament) and Matthew Bates (cruciate ligament) remain on the sidelines.
