Leinster are not in the greatest of shape to easily thwart this latest northern invasion
They have already won Conference B in the PRO14 and have made it this far in Europe for the fifth time in six seasons - yet there is a niggling notion that Leinster are not quite themselves.
This idea has gathered some traction from Ireland's disappointing and rather worrying start and finish to the recent Six Nations when so many of Joe Schmidt's Leinster contingent didn't hit their straps.
And then there is today's selection with no Johnny Sexton in the side, due to injury. That, alone, looks a bit of a game-changer even though Sexton led the way in terms of awfulness in Cardiff.
But that's not all that should be worrying the home supporters as they prepare to gather this evening at the Aviva Stadium.
Rob Kearney and Dan Leavy find themselves benched with Jordan Larmour preferred at full-back and Sean O'Brien making it as the starting openside.
Larmour can expect to be bombarded from the air or at least moved around a lot in the back-field which isn't really his forte while a lot is being asked of O'Brien in a starting back-row that is heavy on the power side - suiting Jordi Murphy - rather than a much purer breakdown presence in Leavy.
And as for Jack McGrath? The experienced Ireland and Lions prop has dropped out of the 23 altogether which, again, hardly instils huge confidence that all is well at team Leinster.
It just adds to the idea that there is vulnerability where there maybe wasn't before.
Though a fairly watered down side lost in Edinburgh last weekend in the PRO14, and shouldn't be held up as meaning an awful lot, there have been signs of apparent frailty during their European season.
Leinster didn't win their pool this time around with anything like the authority they displayed last season. They lost at Toulouse back in October - albeit by one point - which was odd in that they had control of the game but were unable to shut it out as their 10-game winning run in Europe came to an end.
Of course all records must end but then they looked a bit off the money at Bath, in December, before edging that contest through a Larmour moment of magic ahead of just beating Connacht at the RDS and then being turned over at Munster.
The New Year hasn't exactly been hugely convincing either apart from the expected big wins over Zebre and the Kings with the Cheetahs running them reasonably close at the RDS before last weekend's defeat at Edinburgh.
So there is a sense that last season's double-winning side - they bolted on the PRO14 to the Champions Cup - are not functioning just as ruthlessly as before. Mind you, Leinster are still, on the whole, winning games with the huge effort required to beat Connacht in Dublin indicating that they still contain that mixture of x-factor and grit.
And yet you can't help but wonder if Leo Cullen and Stuart Lancaster are a little bit more concerned than they might usually be.
Having no Devin Toner is a blow for his organisational abilities at the lineout, never mind the absent Sexton and continuing concern over Robbie Henshaw's fitness.
A considerable amount of leadership now falls on skipper Rhys Ruddock to get this game done and dusted and he will be heavily relying on dominant displays from O'Brien, James Ryan, Cian Healy, Tadhg Furlong and Jack Conan to get Leinster to the last four.
Garry Ringrose will also have to bring extra influence on the Sexton-less backline with no guiding hand from Kearney at the back.
Ulster's Leinster exiles will have taken note. This is a chance for the visitors and, for once, the champions know it.