Ireland and Leinster captain Caelan Doris will be out of action for up to six months following shoulder surgery, the provincial side announced on Monday.
The 27-year-old sustained the injury in Leinster's 37-34 Champions Cup semifinal defeat to Northampton on May 3.
The backrower was last week left out of the British and Irish Lions' squad for the upcoming tour of Australia by head coach Andy Farrell.
Doris had previously been a frontrunner for the Lions captaincy, which was given to England and Saracens lock Maro Itoje.
"Caelan Doris had a procedure on Friday last week for a shoulder injury which will keep him out of action for between four to six months," Leinster said in a statement.
In addition to the major disappointment of missing what would have been the first Lions tour of his career, Doris is now a doubt for Ireland's internationals later this year.
Ireland, who take on Georgia and Portugal in July, face New Zealand in Chicago on November 1 before hosting Japan, Australia and South Africa in Dublin.