Flanker Sean O'Brien is set to undergo surgery on his hamstring injury and will miss Ireland's three-Test summer tour to South Africa in June.
O'Brien will travel to the United Kingdom on Friday to see a specialist.
The 29-year-old played just six games for Leinster this season, completing 80 minutes on just two occasions.
He signed a three-year contract with the IRFU last December which will keep him at his native province until after the 2019 Rugby World Cup.
At present, there is no indication as to when O'Brien will be able to play again.
"It is too early to say if he can make it back by the start of the season. Initially, he got injured in Ireland's Six Nations game against France and it was a conservative approach in dealing with it," commented Leinster coach Leo Cullen.
"Other guys have been able to rehab similar injuries without surgery, others have surgery straight away.
"It was slower to heal than we would have liked but he broke down and we sought various opinions. It is frustrating but lots of players go through that in their career. He needs a plan in place to get back to the levels he wants. He is such a key figure for Ireland and Leinster."
Another Leinster forward, prop Cian Healy, is unlikely to feature for the rest of the season as he is troubled by a knee problem.
Full-back Rob Kearney misses the Pro12 semi-final against Ulster because of an ankle injury but Leinster say they are hopeful he will be available to play soon.
Ireland head coach Joe Schmidt is unlikely to have winger Tommy Bowe available for selection for the summer tour after it was revealed last week that he is still struggling with his knee complaint.