So here they uncertainly stand. The kings of Europe, with the three stars upon their breasts, are on the brink of devastating elimination or miraculous progress.
Hope, an unfamiliar bedfellow to one of the most outstanding club sides the professional game has ever witnessed, rather than expectancy, tentatively shadows their journey.
Having stuttered and spluttered their way to this point, it is in some ways a testament to Leinster's character and championship spirit that they remain – just – within a hair's breadth of qualification.
Ever since that numbing October afternoon when the champions confidently kicked off their unlikely hat-trick title tilt, before so hesitatingly extricating themselves with a 9-6 victory against today's opposition, this return game loomed large in their thoughts.
"We were very lucky to come away with a win that day because if we hadn't, we obviously wouldn't even be in a position where we could qualify," appreciates Leinster captain Leo Cullen.
What didn't kill them that day may have made them stronger for the challenge that lies ahead this evening, an especially grisly one given the forecasted sleet, driving rain and, perhaps, even some of the snow showers that afflicted much of the south-west of England yesterday.
Definitely not Sandy Park in nature, even if so in name.
Then again, the Leinster dressing-room that huddled so disconsolately together beneath the bowels of Lansdowne Road last month, following a second successive defeat to Clermont, could hardly have contemplated being in a position to essay the potential escapade that lies ahead.
"There was some doom and gloom after the loss to Clermont in the Aviva, a feeling that we were gone," admits Cullen now.
"After the weekend ended, though, you can re-examine the pools and see the way things might unfold. It was important that we clung to that hope. We are still clinging to it to a certain degree.
"Obviously some of the permutations have worked in our favour. No one wants to give up our crown. A lot of work has gone into getting us in the position we have been in the past.
"It's a distracting period during that Christmas/New Year time with national camp too, but I think these two weeks have been at the back of everyone's minds.
"They are very, very important. It determines our season in many ways."
Leinster coach Joe Schmidt, whose only experience of Heineken Cup campaigns in Ireland have culminated in him lifting the trophy, would fancy his side's chances of achieving the improbable in most places. Regrettably, Sandy Park, Exeter is not one of them.
"They've been one of the most consistently difficult teams to beat around," says Schmidt, who has been swift to eke out some inside information from his erstwhile Clermont colleagues after the French giants completed a second demolition of the English side last weekend.
"The Clermont fellas told me they found it very, very tough and possession was pretty evenly shared last weekend, despite the scoreline (46-3).
"Now Clermont have some exceptional individuals who make something out of nothing. I'm sure you saw the try from the kick-off, where they receive it and have Napolioni Nalaga on one wing and Sitiveni Sivivatu on the other and they made something out of nothing.
"Exeter were very much competitive in that game and probably should have scored at 20-3 down and it would have been 20-10 and from there anything could have happened.
"They were 12-10 up against Clermont and they got a yellow card in Sandy Park and that was the start of the slide for them that day.
"So, for sure, there's a lot of other places I'd rather go than Sandy Park this Saturday."
To somehow reach the quarter-finals of the competition they have almost assumed ownership of in recent times, Leinster may have to boldly go where they have never gone before.