Winger Montano has only just returned to the fray for Latics after having a cyst drained earlier in the season, but he will now be kept out of action for a minimum of eight weeks because of a tear in his knee ligament.
The news is also bleak for centre-back Joksts, who will be missing for up to 10 weeks after scans revealed a stress fracture in his back.
Joksts sustained the injury while on international duty with Latvia Under-21s and it was while representing his country that Millar sustained ankle and calf injuries, with the Northern Irishman out for potentially the next three weeks.
Genseric Kusunga misses the next two games due to suspension and, in an attempt to bolster his options for the hectic festive schedule, boss Lee Johnson completed the loan signings of Wade Joyce and Ellis Plummer before the window closed.
- Sports & Recreation