Neptune Collonges will be out of action for a year after he was thought to have suffered an injury in the totesport Gold Cup at the Cheltenham Festival.
The Paul Nicholls-trained grey finished fourth behind Kauto Star last Friday but has sustained a tendon problem.
Owner John Hales told the BBC: “We believe it happened in the race, but it didn’t show up until a few days after.
“It might have been the reason why he didn’t perform at a normal level.”
The three-time Grade One winner will now be assessed by vets – but will not be fit enough to line up in next year’s Gold Cup.
“He now has to have his legs looked at by the vets and the appropriate treatment applied,” added Hales.
“But it means he’ll be off for 12 months, which means he’ll miss the rest of next season as well.”