Sexton benched for Munster semi-final as Cullen favours fresh legs to carry weary Leinster
Leinster v Munster, Guinness Pro14 Championship: RDS Arena, Saturday, 2.30pm
This always looked like a difficult fixture for Leinster and now the shadow of Johnny Sexton looms large over the RDS along with the spectre of Saracens.
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The English team ended both of these provinces' European ambitions for the season and now Leinster and Munster look to the PRO14 for solace.
Both sides measure themselves by their Champions Cup performances, but in a strange way this domestic affair may well define their seasons.
For Leinster, there is a need to keep the flow of trophies going. The double-double is no longer, but back-to-back league titles would be a decent return for a club considered the strongest in this competition by a distance.
As for Munster, this is about showing progress.
They may not admit it publicly, but another semi-final defeat would suggest a club operating at its ceiling and, with half of their coaching team heading for the exit doors soon, there is a need for some positive news.
It's all on the line and Leinster's captain and the reigning World Player of the Year will be watching from the stands as his back-ups at club and international level take centre stage.
After his antics at Thomond Park, where he appeared determined to put Joey Carbery back in his box, he will surely find this an uncomfortable experience.
Leo Cullen says he's done his training, but the head coach has opted to select Ross Byrne as his starting out-half instead.
Perhaps the toll of a bruising 80 minutes against Saracens meant the out-half would not be at his optimum performance levels, but the decision has worrying ramifications for the autumn when Joe Schmidt will need him to go back-to-back for three weeks if Ireland are to compete for the Webb Ellis trophy.
Step forward Carbery, who has played just 32 minutes since February but makes a timely return to the RDS for the first time.
He started this fixture in blue, at full-back, last season and left for more opportunities to play out-half in order to enhance his prospects of challenging Sexton for the Ireland shirt.
It seemed almost fanciful at the time, but a year on the idea of a real rivalry in Japan is no longer far-fetched.
After his epic 2018, Sexton, 33, has come back to the pack dramatically and his position now looks more vulnerable than ever.
Schmidt and his coaching team will be tuning in with interest.
Not only is the battle of the back-ups fascinating, so too is the presence of CJ Stander as Johann van Graan goes full Springbok.
Eagle-eyed fans will have noted how the South African-born back-row packed down in that role for Ireland when he played with Jack Conan.
He has the physical attributes to do the job in tandem with breakdown threats Peter O'Mahony and Tadhg Beirne, but the lack of an out-and-out No.7 is a risk as Josh van der Flier comes in for Seán O'Brien - one of three centrally-contracted players left out of the match-day 23 by Cullen, who has gone for a young and dynamic side.
O'Brien trained on Thursday but missed last week's collision-fest, while Rob Kearney and Jack McGrath were left out.
Cullen is hoping the freshness of fit-again Van der Flier, skipper Rhys Ruddock, Dave Kearney and Byrne can inject life into his battered team.