Wayne Pivac's Scarlets will have to do without captain Ken Owens for their crunch Guinness PRO12 semi-final with Leinster on Friday evening.
Ireland and Lions back rower Sean O'Brien is suffering from a tightness in his calf and a decision has been taken not to risk the injury further.
Hooker Owens, who is set to tour New Zealand with the British & Irish Lions this summer, suffered an ankle injury in training this week and won't run out in the Irish capital.
In better news for Scarlets, back row pair James Davies and John Barclay have recovered from respective knocks to return to the starting XV, with Scotland worldwide Barclay named as captain.
Leinster v Scarlets semi-final tickets are still on sale via leinsterrugby.ie or at the RDS from the Anglesea Road ticket office. They're scoring a lot of tries themselves at the moment and it makes them a pretty complete package. "We haven't been in this position since this group of coaches, and players, have been together".
"It will be a big, big challenge for us but it's also a great opportunity".
"It's a big task but it's one we're relishing having", Pivac told the Scarlets official website.
Leinster: Joey Carbery; Adam Byrne, Garry Ringrose, Robbie Henshaw, Isa Nacewa (capt); Johnny Sexton, Luke McGrath; Jack McGrath, James Tracy, Tadhg Furlong, Ross Molony, Hayden Triggs, Rhys Ruddock, Josh van der Flier, Jack Conan.
Scarlets: 15 Johnny McNicholl, 14 Liam Williams, 13 Jonathan Davies, 12 Scott Williams, 11 Steff Evans, 10 Rhys Patchell, 9 Gareth Davies; 1 Rob Evans, 2 Ryan Elias, 3 Samson Lee, 4 Lewis Rawlins, 5 Tadhg Beirne, 6 Aaron Shingler, 7 James Davies, 8 John Barclay (c).