Ruby Walsh will partner Long Run for the first time in Sunday's Grand Steeple-Chase de Paris at Auteuil.
Sam Waley-Cohen, son of the owner Robert, has been ever-present in the saddle since the nine-year-old joined trainer Nicky Henderson five years ago, guiding him to glory in the 2011 Cheltenham Gold Cup and successive renewals of the King George VI Chase at Kempton.
However, the Grade One contest forms part of the popular 'Quinte' bet (based on predicting the first five horses home in the correct order) on Sunday and French rules do not allow amateurs to ride in such races, which means Waley-Cohen cannot take the mount.
Robert Waley-Cohen described the situation as "very disappointing", but is pleased to have secured the services of Walsh in the plate.
He said: "He's in great form. He schooled at Chantilly on Thursday and was absolutely outstanding, so we decided to let him take his chance.
"It's very disappointing Sam is not being allowed to ride him and, in my opinion, the reasons are invalid. Just because you don't get paid to ride doesn't mean you don't have talent or the ability to do it.
"When people are betting they know who the jockey is, whether they like him or not, and they can decide whether they want to back the horse or not.
"Sam is obviously very disappointed as he's ridden in the Pardubice, the Grand National and the Maryland Hunt Cup this year and he's not being allowed to ride this weekend.
"We've booked Ruby Walsh and I believe it will the first time he's worn my colours.
"He has never ridden Long Run before, but he is a vastly experienced jockey and it made sense to have him ride as he is already over there to ride for Willie Mullins.
"Sam will be there so he can tell Ruby about the horse and we're looking forward to the race.
"Long Run is already a French champion and we know he loves Auteuil.
"They've increased the distance of the race to three miles and six furlongs this year, which I think will suit him."
Long Run will be joined by Jo Hughes' Soll, who was last seen finishing unplaced in the Topham Chase at Aintree last month.
Mullins may not be represented in the main race, but he fields four runners in the Grade Two Prix La Barka.
Walsh will be aboard Diakali, who was only narrowly beaten in the Aintree Hurlde, while his sister Katie rides Thousand Stars, winner of the race in 2012.
Paul Townend teams up with the mare Glens Melody leaving David Casey to partner Zaidpour.
Paul Nicholls' Zarkandar also takes his chance with the Ditcheat trainer having booked local star David Cottin for the mount.