Kieren Fallon retired from the saddle after suffering with depression for the "the best part of three years".
The Irish Turf Club's chief medical officer Dr Adrian McGoldrick revealed the 51-year-old's illness had gone unnoticed when he was riding in England and America.
County Clare-born Fallon has returned to his homeland this season, and has now sought medical advice to help combat "quite profound depression".
Dr McGoldrick told Press Association Sport: "I first became aware of it when he came to see me for his licence earlier this year and he was obviously very significantly depressed.
"Kieren's had quite significant depression ongoing for the best part of three years which has gone undiagnosed in England and America.
"It got worse and I met with him on Sunday and have arranged to have it managed.
"He went to see a specialist in America and nobody picked up on it.
"It's quite profound depression. As soon as I can get a bed organised for him, he'll be going to hospital here in Ireland.
"Hopefully we can get him managed and get him ready for the next stage of his life.
"He said he won't be returning to race riding afterwards and will move on to another phase of his career, whatever that might be.
"He felt himself he had no motivation for the last two or three years and that had affected his depression. At this stage of his life he feels he has to move on.
"We know that a lot of elite athletes have depression. I commissioned a survey in racing last year and 49 per cent of jockeys in Ireland actually had symptoms of depression."
Kieren Fallon has retired from racing at the age of 51. He was Champion Jockey six times an won 15 Classics. Legend. pic.twitter.com/zgV3EKKf0B— 888sport (@888sport) July 4, 2016
Fallon, a six-times champion jockey in Britain, will continue to play a part at the yard of young Curragh trainer Michael O'Callaghan, with whom he has been attached since his return from America in the spring.
O'Callaghan said: "He had a fall on the gallops last week and he just said he's 51 now and doesn't bounce like he used to.
"Kieren has been a great asset to have around the yard.
"He rode his first Group winner for a long time for us not too long ago.
"It's been great to have him here and he is going to remain here as a work rider and advisor, hopefully for a while to come - he's just giving up the race riding.
"He's had an amazing career on the track - he must be one of the best jockeys of all time.
"He is worth his weight in gold to us here, but the main thing is that we just want what is best for Kieren."
The three-times Epsom Derby winner's last ride in public came on June 26, when he rode O'Callaghan's Magical Fire to finish fifth at the Curragh.
Fallon was widely regarded as a master of his trade in his pomp and claimed 16 Classic victories in Britain and six in Ireland.
During his halcyon years, he was also attached to powerhouse yards of the late Sir Henry Cecil, Sir Michael Stoute and Aidan O'Brien.
His career was often blighted by controversy, though, and in October 2007 he was embroiled in a two-month-long corruption trial at the Old Bailey.
Fallon was unable to ride in Britain until the end of the trial, but he was cleared of all charges in December of that year.
But one month later he was given an 18-month worldwide ban from racing after he tested positive for a banned substance - the second time he had been suspended for failing a drugs test - following a race at Deauville in August 2007.