Oldham star James Wesolowski could miss up to five weeks after boss Lee Johnson confirmed he had fractured his cheekbone.
It means the 26-year-old is highly unlikely to play in the money-spinning trip to Liverpool in the FA Cup third round on January 5 after sustaining the injury in Tuesday's second-round replay win over Mansfield.
Johnson was fuming with the blow the midfielder received to the face after 24 minutes from Jamie McGuire, with the Latics boss suggesting the Stags player had done it on purpose.
"It's not good," Johnson said of Wesolowski's injury.
"It's a fracture on his cheekbone and I was disappointed with the refereeing decision at the time. I was close to it and I thought there was a fair amount of intent there. Whether or not I'm right I don't know, but that was my instinct.
"I went to see him in the hospital, we had a long old day yesterday (Wednesday). He didn't finish until 2.30 in the afternoon.
"However, it is the best case of a fracture, so best-case scenario is he will be three to five weeks just resting and maybe we can get a special mask made up for him.
"Weso wanted to play on and I'm pleased his eye swelled up because it could have been dangerous.
"He's such a hard, tough little cookie and had he taken another blow that could have been really bad for his vision or skull.
"His eye closed up that much he was literally playing on with one eye."