Jockey Jason Maguire, who won the Grand National on Ballabriggs in 2011, is to retire aged 36 after serious injuries.
The Irishman has not ridden competitively since February 2015 after a fall at Musselburgh.
Maguire suffered a serious injury a year earlier which left him in an induced coma.
Agent Chris Broad said: "He was a top-class rider - it wasn't long ago that he split AP McCoy and Richard Johnson in the championship."
He was seriously injured in a fall at Stratford on the eve of the 2014 Cheltenham Festival, suffering internal bleeding, a fractured sternum and having part of his liver removed while in an induced coma.
Maguire underwent surgery last April for slipped discs in his back and while he has been riding for the likes of Kim Bailey and Tom George, he was often left with a pain in his leg.
Having ridden as first-choice jockey for owners Paul and Clare Rooney, during his time off he has been acting as their racing manager.
Confirming his client's retirement, Broad said: "It's disappointing, but the news has been expected, to be honest."
The retired 20-time champion jockey AP McCoy paid tribute.
"For the last six months he was riding in unbelievable pain, he was having to travel to the races lying down in the back of cars it was hurting so much," he said.
"He was an unbelievably tough competitor and, if anything, he was getting better with age."
Analysis - BBC horse racing correspondent Cornelius Lysaght
"To know the quality of Jason Maguire, nephew of ex-jump jockey Adrian, you just have to know he was rated an outstanding rider in an outstanding period - the era of AP McCoy, Richard Johnson, Ruby Walsh and Barry Geraghty.
"If there was one skill that shone above the others it was his strength in a finish; his mounts were always hard to pass.
"Though their association ended unhappily, the link with trainer Donald McCain was particularly prolific and included a memorable success on Ballabriggs to put the McCain family (of Red Rum fame) back in the Aintree spotlight."