If there is one man Joe Schmidt cannot do without for the Six Nations it is Jonathan Sexton.
When Ireland's out-half took an accidental blow to the head from former team-mate Brendan Macken in the ninth minute of Leinster's submission to Wasps, he was forced to the all-too familiar examination of a Head Injury Assessment.
After Sexton did not return, Leinster failed the test without him, failed their coaches and failed their supporters in what would best be described as 40 minutes of humiliation, sucking in 36 unanswered points.
England international James Haskell summed it up succinctly: "It's not rocket science," he reviewed.
"If you watch Leinster play, Johnny Sexton is such an influential player. When he is on form, he can be devastating.
"It is the same for when he plays for Ireland.
"Obviously, you never want to see a player go off, but there was a sigh of relief when we saw that."
For all of his replacement Cathal Marsh's gifts - and there are many - this was like being thrown into a lion's den with the bare minimum of rugby experience to draw on.
The bigger picture demands a thorough inspection of Sexton's history with concussion. It is a high-profile and high-cost situation.
The former Racing Metro man has been concussed on a number of occasions in the last two seasons, most seriously when forced away from the game for 12 weeks in the winter of 2014.
He returned to action for Ireland in the 2015 Six Nations, coming in cold against France to claim five penalties and a Man of the Match accolade.
There are question marks hanging like an axe over Ireland prop Martin Moore too.
For the most part, he was solid at scrum time against England's highly-rated Matt Mullan.
However, Moore was assisted from the pitch with a hamstring strain that must endanger his participation for Ireland, for at least the first two matches.
It has been a badly handled few weeks for the tight-head as he became embroiled in a distasteful tug-of-war between Wasps and the Irish Rugby Football Union.
Apparently, the 24 year-old had agreed terms with the English Premiership club before the reported, but unconfirmed, intervention of Elite Performance Director David Nucifora and Schmidt forced a rethink.
The severity of the hamstring injury could throw another factor into the 'will he, won't he' move.
Minimally, Ireland's posse of tight-heads has been reduced to a party-of-two for what is certain to be a hard-charging Wales on Sunday week.
Mike Ross was left out of the extended squad with a hamstring issue of his own for the first two internationals, leaving Connacht's Nathan White and Leinster's Tadhg Furlong in competition to don the number three shirt.
Turning back to Leinster, it was one of those wounding occasions at the Ricoh Arena when a coach had to walk out of the mire of mediocrity to explain the unacceptable.
"We had a lot of high hopes going into this competition this year but, in the games against Wasps, we've been well and truly second place," said coach Leo Cullen. "It was a little bit like our game in round one at The RDS where we start chasing the game very, very early.
"Wasps just defend with most of the players in a line," he continued.
"We end up forcing passes, not respecting the ball and, as a result, when we turn the ball over, very cheaply on a couple of occasions, Wasps then go the length and score."
Breaking records is not always good news.
Overall, this was Leinster's worst European campaign on so many fronts, none more relevant than the widest losing margin in their storied history.
Not even the heavily maligned 'The Ladyboys' were charitable enough to give up a 41-point chasm.
It was just the second time Leinster's dam was busted for more than 50 points.
You have to go all the way back to October of 1998 to uncover the first.
At least, Leinster then had the decency to strike for 31 points when they lost 56 of them to Stade Francais at Stade Jean Bouin.
The previous worst margin was 36 points as Leinster eclipsed the harrowing 43-7 loss to Toulouse in January 2002.