Iain Henderson will miss the majority of Ireland's Six Nations campaign.
The second row has been ruled out for between 10 and 12 weeks after undergoing thumb surgery today.
Henderson has been in fantastic form of late, scoring a pair of tries in Ulster's Heineken Champions Cup win over Scarlets on Friday.
The surgery also means Henderson will miss Ulster's final two Pool 4 games in Europe.
Ireland's 2019 Six Nations campaign will kick off against England on February 2, with the final game away to Wales on March 16.