Conor McMenamin is facing two months on the sidelines after it was confirmed he suffered a broken metatarsal in Sunday's defeat to Cliftonville.
The 27-year-old limped off after picking up a knock just 24 minutes into the game against the Reds.
McMenamin had an MRI scan done earlier this week and met with a specialist today where the full extent of the injury was confirmed.
Read more: McMenamin admits new injury concern as he opens up on 'fracture' saga
It means McMenamin is unlikely to return until round February time, depending on his recovery.
It is a huge blow for the Glens who will be without the talismanic winger for the busy Christmas and New Year period.
Mick McDermott's side are right in the title mix this season, sitting just six points off leaders Larne but with two games in hand.
It is a huge blow for McMenamin himself, with the Northern Ireland winger being tipped for a New Year move across the water.
Speaking to Belfast Live on Thursday, McMenamin said he feared the worst over the injury, which is unrelated to the knock he sustained against Coleraine which was initially reported as a fractured fibula.
"It is my foot. I have to see a specialist in the morning. It's not good," McMenamin said.
"It came from a tackle on Sunday. I knew straight away something wasn't right. It didn't feel right and I signalled to come off straight away.
"I had tried to play on but I couldn't put weight through it and it's still not great."
He added: "Obviously I have been playing pretty well and I want to help the team, but on Sunday the foot just wasn't right after the tackle.
"Hopefully I will be back sooner rather than later, but at the minute I just don't know.
"I had an MRI during the week and I am due to see a specialist on Friday morning who is going to assess things."
Meanwhile, Glentoran could also be without forward Shay McCartan for seven games following his sending off against Cliftonville.
McCartan's three-game ban is set to be extended because of his protests to the match officials.
McDermott told the BBC: "At this moment I know the disciplinary panel will be sending out a letter.
"I'm not sure if we received that letter last night or will do this morning.
"A straight red card is usually three [games]. You can appeal all the decisions.
"I will have to look at the referee's report which I haven't seen yet but if it was three plus four, I think anyone would consider that very lengthy, especially if it was for any verbal communication with a linesmen or the referee.
"I've been in Irish League games for a wee while now and some of the language I would say is colourful."
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