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."
Henderson enjoyed an impressive Rugby World Cup and had been set to fill the void left by Paul O'Connell in Ireland's second row.