But McDonald's injury is not as bad as first feared and he could return inside a fortnight.
The 27-year-old limped off during Tuesday night's SPL defeat at St Johnstone and looked set to be ruled out for the rest of the season, but he might only miss Satutday's match with Dundee United and the following weekend's game with St Mirren.
Captain Mark Kerr has shaken off a sore groin to play tomorrow, while Peter Pawlett (knee) and Andrew Considine (hip) are long-term absentees.
Aberdeen (from): Langfield, Foster, Diamond, Mulgrew, Paterson, Kerr, Aluko, Fyvie, MacLean, Mackie, Paton, Ifil, Duff, Nelson, Young, Marshall, Grassi, Megginson.
