The New Zealand equestrian Andrew Nicholson has undergone surgery on his neck following a fall at the weekend.
Nicholson, one of the most successful riders in eventing history, is in an Oxford hospital recovering and has a full range of movement.
The 54-year-old fell from Cillnabradden Evo at the Festival of British Eventing at Gatcombe Park.
He was taken to hospital in Swindon after the cross-country fall, then transferred to Oxford's John Radcliffe Hospital.
A family spokesperson said the surgery was to repair the injury to his neck.
She said the surgery went well and his condition was stable. He was comfortable and had a full range of movement.
The former world number one has won three Olympic team medals with New Zealand, as well as three World Championship medals.
Nicholson is also a five-time winner at Burghley Horse Trials in Lincolnshire.
BBC Wiltshire eventing journalist Barbara Gale was at Gatcombe and said a witness told her Nicholson's horse had cleared the fence, then seemed to stumble.
Both horse and rider landed extremely heavily.
"One of our listeners came up to me and said, 'It was the most awful thwack, it was one heck of a fall', Ms Gale told Morning Report.
"Both the horse and the rider, the spectator and listener told me, he did get up but then Andrew didn't seem to know where he was or what he was doing.
"And very quickly, apparently, three ambulances arrived."
Ms Gale said Nicholson's wife Wiggy was with him at hospital. She said the extent of his injury has not been made public.
Nicholson first represented New Zealand at the Olympics in 1984 and is the fifth ranked eventer in the world.
Equestrian Sports New Zealand eventing chairman Todd Gloyn said Nicholson's career was unsurpassed in the equestrian world.
He said people were shocked to hear of his fall and said Nicholson was a "tough person" and a "tough competitor".
The organisation's high performance operations manager Warrick Allan said Nicholson was known as "Mr Stickability" and there had been a huge outpouring of support on social media from his fans in New Zealand and in the UK.
The family's spokesperson said the horse was not injured in the fall.