Sean O'Brien will not feature in Ireland's 2019 World Cup campaign after sustaining a hip injury, which will rule him out for up to six months.
The 32-year-old injured himself during Leinster's Champions Cup final defeat to Saracens and will undergo surgery.
O'Brien has now played his last game for Leinster after it was confirmed in February that he would leave the Pro14 side at the end of the season to go to Guinness Premiership side London Irish.
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The back row has 56 caps for Ireland and has made 123 appearances for Leinster since he turned professional in 2008.
After taking the decision to depart Leinster, O'Brien said the move to London Irish would not affect his desire to play international rugby for Ireland in the future.
Leinster claimed their sixth PRO14 title with a hard-fought 18-15 win over Glasgow at Celtic Park on Saturday.