Jack Conan will miss the 2020 Six Nations after surgery on the foot injury that ended his World Cup early.
The Leinster flanker went under the knife last week and the province today confirmed the 27 year-old will be out of contention for 'up to six months'.
Conan was pencilled in to start Ireland's shock Pool defeat to Japan, but was ruled out after suffering the injury in training.
“The timeline there doesn't look great, it's a significant period out for him, obviously on top of Dan [Leavy],” said Leinster boss Leo Cullen.
Leavy, who suffered a horror knee injury in the Champions Cup quarter-final win over Ulster last April, is expected to miss almost the entire season, while Seán O'Brien joined London Irish in the summer, further diluting the province's backrow options.
Josh van der Flier and Rhys Ruddock, who were involved in Ireland's quarter-final hammering to New Zealand at the weekend, are likely to return to action in time for Leinster's Champions Cup opener against Benetton on November 16.
Leinster are in the dark over Seán Cronin's availability, after the hooker's World Cup involvement ended early with a neck injury.
“We're getting Seán assessed,” Cullen said. “I don't know the strength of that [injury] so he will be further assessed, but he's not ready for Saturday against Zebre.”
Out half Ciarán Frawley has returned to training after an ankle injury but will also miss out this weekend.