Popular jumper Un De Sceaux has suffered a career-ending injury just days out from what would have been his sixth Cheltenham Festival.

Trainer Willie Mullins described him as a once-in-a-lifetime horse after deciding he should be retired immediately when the injury was discovered after a gallop.

The 12-year-old finished outside the first two just once in 21 completed runs over fences - the majority of which were in Grade One company.

"Right up to the end, he was trying to impersonate a four-year-old," Mullins said.

"You could see on pulling up that he wasn't right, and it was confirmed this morning that he had a ligament injury."

Un De Sceaux has been among the brightest stars at Mullins' powerhouse stable since arriving from France seven years ago.

"You can't replace horses like him," Mullins said.

"It's impossible. He was a once-in-a-lifetime horse, and we were very lucky to have him."

Un De Sceaux ran at five Cheltenham Festivals, winning the Arkle in 2015 and the Ryanair in 2017.

Owner Edward O'Connell's son, Colm, said Un De Sceaux would live out his days in France.

"This day was always going to come - but we'd planned to go to Cheltenham and retire him on the spot," O'Connell said.

"He'll go back to France in a couple of months. Ginnie (Virginia Bascop) who looks after him has a plan to take him back there. You don't put Eric Cantona in a nursing home."