Ireland international Iain Henderson will not be available for selection when his country competes in the Six Nations, which kicks off in early February.
Henderson, who is expected to return to the fray for the Summer tour of South Africa, sustained a hamstring injury last December and it has since become increasingly clear that he will not feature in his national team's title defence.
"It looks like Iain will be out for the remainder of the season," Ulster coach Neil Doak told journalists this week.
"It's unfortunate, but that's the way it is," added Doak.
In addition, the Irish rugby fraternity has been forced to contend with the reality of Winger Tommy Bowe being absent from international duty, after he told the BBC that his hopes of competing internationally this season had been doomed.
"Unfortunately it's a slow process and to rule yourself out of the Six Nations is disappointing," said Bowe, who is still recovering from a knee surgery.
"I have to concentrate on getting myself back to where I was and there's no point in rushing it," added Bowe.
"To be back by the start of February is unlikely but I'm still pretty positive I can add something to Ulster's season," added the Ireland international.