Vodafone Derby winner Motivator will be retired to stud after being ruled out of the Breeders´ Cup Turf through injury.
The son of Montjeu was found to be slightly lame on his off-hind leg after doing his final piece of work at Newmarket in preparation for the big race at Belmont Park next Saturday.
The Michael Bell-trained colt was syndicated earlier this month for #6million to stand at the Royal Stud at Sandringham.
Harry Herbert, racing manager to owners the Royal Ascot Racing Club, said: 'He worked absolutely brilliantly in his final piece of work but pulled up slightly lame behind.
'It was nothing life-threatening but it was enough to put him out of the Breeders´ Cup and therefore signal the end of his racing career.
'We are all desperately disappointed because we felt he had a great chance of taking the race in America by storm.
'But sadly something went amiss which is a career-stopping injury.'
While Herbert could not hide his disappointment at the three-year-old´s enforced retirement, he acknowledged Motivator had provided the Royal Ascot Club with memories to cherish forever.
'It´s tragic news but I would like to go on record as saying what a marvellous job Michael Bell and his team have done with Motivator in making this last season so remarkably special,' he added.
'Michael´s work in allowing the racing public to savour the build-up to the Derby has made the horse one people have grown to love.
'We are all very proud of what Motivator has achieved and he has given us the greatest thrill in racing, which is to win the Derby.
'The great swathe of support that was shown when he won the Derby spoke volumes about his popularity.
'He had so much speed and brilliance and was a great character who loved racing.'
Motivator raced seven times, winning both his starts as a two-year-old including the Group One Racing Post Trophy at Doncaster exactly 12 months ago.
He made a successful reappearance in the Dante Stakes at York in May before achieving his finest hour when romping home by five lengths in the Derby at Epsom the following month in the hands of Johnny Murtagh.
That turned out to be the last of his four victories as he finished second in the Coral-Eclipse Stakes and the Irish Champion Stakes behind Oratorio, before finishing fifth to Hurricane Run in the Prix de l´Arc de Triomphe at Longchamp earlier this month.
The son of Montjeu earned prize-money totalling #1,192,457.
Bell told Channel 4 Racing: 'He worked really well, as well as as ever worked. He was in great form and walked home sound but then when we got him back to his box we found he was slightly lame on his off-hind so it has knocked the Breeders´ Cup on the head, sadly.
'For this to happen is gutting for all concerned, especially as he was primed and ready to go. He was amazingly consistent in all his starts.'
Murtagh was fulsome in his praise.
He said: 'He was great on Derby day and nobody can take it away from him. He gave us a great thrill that day and it´s just unfortunate the way things have gone because I had a feeling Belmont would really have suited him.
'He was a very good horse and on Derby day it would have taken a very good horse to beat him.
'The way he handled the track, the way he did everything. I rate him highly. He was very good on the day. He had speed, stamina and everything required for a Derby winner.
'He was highly strung but as soon as he got out and in the parade he was very professional.'
Of Motivator´s budding stud career, Herbert added: 'He is fully syndicated by a great group of owners and breeders and I am sure he will enjoy a lot of success at stud.
'He will be prepared for covering in February by some of the best breeders in the world and I´m sure he´ll have a fantastic first book of mares.
'Motivator has got the looks, the charisma and the pedigree to make a fantastic stallion.'
Motivator had been 5-1 third favourite with William Hill for the Breeders´ Cup Turf.
Azamour is now 5-2 market leader with Hills and 11-4 with Ladbrokes in the revised market.
? PA Sport
