Ireland forward Iain Henderson has been ruled out for nearly three months to leave his participation in the Guinness Six Nations in doubt.
The 26-year-old underwent surgery on a torn ligament in his thumb on Monday, with Ulster announcing he is expected to be out for "approximately 10 weeks".
Henderson scored two tries for Ulster in Friday's 30-15 Champions Cup victory over Scarlets but will now miss the region's final two Pool Four games as well as a number of Guinness PRO14 fixtures.
He is also stands to miss Ireland's Six Nations home game against England on February 2 and the trips to Scotland and Italy on February 9 and 24 respectively.
If the 10-week time-frame proves accurate he could come into the reckoning for the final two matches, at home to France and away against Wales, in March.
By having the surgery now Henderson is hoping to have the injury well behind him in time for the World Cup in Japan in September.