Jack Conan has been ruled out for six months after sustaining a foot injury at the Rugby World Cup, Leinster have confirmed.
Conan was selected to start Ireland's Pool A loss to Japan, but broke his foot in training two days before the game and was replaced in the line-up by Peter O'Mahony.
The No 8 was subsequently ruled out of the World Cup, and on Monday Leinster coach Leo Cullen confirmed Conan underwent surgery on his foot last week.
It means the loose forward will miss Ireland's 2020 Six Nations, their first with new head coach Andy Farrell at the helm.
Farrell takes over from Joe Schmidt, who stepped down from the role following his side's exit from the World Cup at the hands of New Zealand in the quarter-finals on Saturday.