Gillingham captain Barry Fuller will not return until April after suffering a broken arm against Leyton Orient.
The right-back has seen a specialist who assessed the injury he sustained during the 1-1 draw with Orient six days ago and the diagnosis has ruled Fuller out for between four and six weeks.
"It is not good news," Gills boss Mark Stimson told the Kent Messenger.
"After four weeks he may get a light cast on it but that depends on how it is healing. He should possibly come back before the end of the season."
Stimson believes Saturday's 2-0 defeat at Carlisle illustrated just how big a loss Fuller will be.
He added: "It is a hard one to fill because I don't think people realise how good he has been this year.
"It is a massive loss but we can't do anything about it and we have to get on with it.
"We will see if people can step in and take on that challenge and if they are half as good as him that would be enough."