Leinster flanker Sean O'Brien's season is over after he underwent shoulder surgery today.
The Carlow man has had a miserable year with injury, playing just 67 minutes of rugby since December, including 40 minutes against Benetton last weekend.
After a minor hip operation in January ruled him out of the start of the Six Nations, a subsequent shoulder issue saw him sit out the rest of Ireland's Grand Slam triumph.
That same problem has now taken the 31-year-old out of contention for the business end of the Champions Cup and Pro 14 campaigns.
"Sean has been ruled out," head coach Leo Cullen said at the announcement of his team to play Scarlets in the European semi-final tomorrow.
"He didn't come through (training) this week. He's had a procedure done on his shoulder today.
"We'll find out the full extent (of the recovery period) over the next few days."
There was better news on Luke McGrath's ankle issue.
The scrum-half misses out on a place in the squad tomorrow but has almost recovered and should be in contention for the trip Connacht on Saturday week.
"Luke is making good progress," said Cullen.
Follow Leinster v Scarlets via our live blog on RTÉ.ie and the News Now App (kick-off 3.30pm), or hear live updates on RTÉ Radio 1's Saturday Sport. Follow Racing 92 v Munster (kick-off 3.15pm) via our live blog or listen to live and exclusive radio commentary on RTÉ Radio 1's Sunday Sport.
