Chris Burton's excitement at the prospect of winning an individual Olympic eventing medal for Australia has been tempered by his sadness over a teammate's injured horse on a dramatic day of cross country at the Chateau de Versailles.

Kevin McNab decided to retire his horse Don Quidam during Sunday's round after he sensed his Olympic silver-winning mount from Tokyo three years ago may be lame.

His decision to pull out Don Quidam was proved correct when the team vet discovered the horse had suffered a soft tissue injury.

The most important news was that a fully recovery was expected.

"The horse was going really well and he just landed a little awkwardly in the last water and I felt it when he came out," McNab said.

"In the best interest of the horse, I decided to pull up."

The retirement meant the end of the Australian trio's bid to win another medal in their traditionally strong event but was widely applauded because of McNab's first concern being the animal's welfare.

Burton, the last of the three to jump, admitted to his own mixed feelings after he then delivered a superb, faultless round on Shadow Man to move into outright third place in the individual standings with his strongest discipline, the showjumping, to come on Monday.

"It's a gut-wrenching sport, isn't it?" Burton said.

"We turned up here with three really good riders on three very good horses. And when our pathfinder (Shane Rose on Virgil) went out and went so well, you can't help but get a little bit excited.

"I sit here sort of feeling happy, but with mixed emotions, because I'm so devastated for our colleague Kev and his beautiful horse — and hopefully the horse is okay."

As for McNab's sadness, Burton was determined to rally round and cheer up his pal.

"We'll go and make sure he's all right, but he's tough. It's just devastating for him," he said.

McNab and Rose were part of the silver-winning trio with Andrew Hoy in 2021 but their chances of a repeat have gone now with the 200-point penalty for a retirement. Reserve Shenae Lowings will step in to complete the jumping phase on Monday.

AAP