Last year's Prix de l'Arc de Triomphe winner has never raced over a trip as short as a mile before, having begun his career in a mile and a quarter race at Evry in March last year and having rarely strayed below a mile and a half since.
He contests tomorrow's Group One race not because it is the belief of his trainer, Elie Lellouche, that racing over a mile is the perfect preparation for defending the Arc in his next race, but because his owner, Enrique Sarasola, says so.
So can this exceptional performer at middle-distances display the same devastating power over a mile? Modern-day trainers hardly ever ask their best horses to revert to shorter trips once they have proved they can last the "Classic" distance of a mile and a half, and it is no coincidence that Europe's most important and most valuable races, the Arc and the Derby, are run at that trip.
Many horses are asked to step up in distance as their careers progress -Desert King has won Irish Classics at a mile and then a mile and a half this season - but very few attempt to revert to shorter trips.
Yet trainers often claim that their very best horses are speedier than their sprinters on the gallops and would be top-class performers at whatever trip they tackled. The physical characteristics of a long-backed, long- striding stayer are different from that of a well-muscled, wound-up sprinter, but they are not that different.
What is greatly in Helissio's favour is that he is back on his favourite track and back with Olivier Peslier on board. Cash Asmussen rode the colt when they were only third to Swain at Ascot last time.
"Helissio is in his garden at Longchamp and he gallops freely for Peslier," Lellouche said this week. "If the decision had been mine, his Arc trial would have been in the Prix Foy [next Sunday]. But I think he has enough speed for a mile and I am optimistic."
Spinning World, so impressive at Deauville last time, is the obvious alternative to Helissio, in a race which sees the return to action of Mark Johnston's Bijou D'Inde, who has been off the track since injuring himself in the Dubai World Cup in April. The race may lose the other British representative, Rebecca Sharp, if the going, currently good to soft, is deemed too testing by Geoff Wragg.
BBC2 plan to show a recording of the Moulin during Sunday Grandstand.
The Grosser Preis von Baden would have been another alternative for Helissio but for his aversion to travel. In his absence, the British-based Luso and Predappio have strong chances of fighting out the finish of this Group One prize.
The third race of the day at the top level, the Moyglare Stud Stakes at the Curragh, sees four Aidan O'Brien runners take on the rest of the world, well eight others. Lady Alexander, the Molecomb Stakes winner, looks superior.