The forty-eight year old rider suffered a crashing fall at Wolverhampton in July, breaking seven ribs and fracturing the T6 vertebrae, and has struggled to recover fully from the injuries.

O'Neill achieved 1,889 winners in the UK throughout his career, and is best-known for his association with the Shadwell operation. In 2012, he earned the role of second jockey for Sheikh Hamdan Al Maktoum, winning the Commonwealth Cup on Muhaarar and the September Stakes with Mostahdaf in the blue and white silks.

"I've given it a good go but unfortunately it is just not healing. There's quite a significant gap between the vertebra and there was damage to the other vertebra as well," said O'Neill.

"It's filled in a little bit, but not enough and it is mainly filled with scar tissue, so it wouldn't take another impact.

"But on a positive note, because I broke seven ribs as well, once I healed and it stabilised, I've never really suffered any pain and I'm leading a normal life, so I've got to be thankful for that.

"I got 32 years out of it, so while it isn't the way I wanted to end it, it's a good chunk of time. I was watching some old races back the other day and there's only John Egan still going now.

"The writing has been on the wall, I'm 48 so I wasn't going to get another 10 years or anything, but 32 years has been a fair chunk of my life, so I'm thankful.

"I only had three jobs in all that time. I started out with Richard Hannon and I still ride for young Richard now. Henry Candy then made me his stable jockey and he was the first person to congratulate me after I won the Commonwealth Cup on Muhaarar, which was nice – especially as he was second with Limato!

"Then I moved on to Sheikh Hamdan and Sheikha Hissa, who was kind enough to leave things as they were, even when they downsized the operation and they probably didn't need a second jockey. I was pleased to ride her three Grade Ones in Dubai."