Dettori was on the Godolphin filly Shawanni before the Ballymacoll Stud Stakes when she reared over backwards on to her rider on the parade ring's tarmac path.
His left elbow took the impact of the fall and he sat on the ground for several minutes receiving medical attention before being taken by stretcher into an ambulance.
Despite his obvious pain, Dettori remained cheery. "I broke the other one a long time ago, so I know what it feels like," he said. "My left elbow doesn't feel too good and I feel a bit shaky."
The champion jockey was taken to the Royal Berkshire Hospital in Reading where an X-ray examination confirmed that he had broken his elbow.
Dettori, champion for the last two years, has had a campaign interrupted by suspensions and has been left trailing by Pat Eddery by 12 wins. But he was back at the peak of his form on Wednesday when riding six winners in a day for the first time and devoted some of his time at Newbury yesterday to supporting the Dorset-based Fortune Centre of Riding Therapy, his charity of the year.
His accident was witnessed by Alan Dadswell, a race-reader with Superform, who was standing just a few feet away. "As soon as Frankie got on the filly she planted herself," he reported. "He managed to get her to move but then she went sideways into the rail and straight over backwards."
Two of the main equine attractions at Ascot went through their paces yesterday, both pleasing their trainers and confirming their passage to Berkshire. Double Trigger, the Ascot Gold Cup favourite, delighted Mark Johnston in his final serious workout before attempting the double in Thursday's race.
Double Trigger, under Bobbie Elliot, led the Johnston string in a five- furlong canter before getting down to the serious stuff alongside the Queen's Vase entry Lallans over a mile and a half on Middleham High Moor.
"That was perfect," Johnston said. "We just need a trouble-free run between now and Thursday. Today will be the last time he goes upsides another horse."
The days leading up to the race will be of particular concern to Johnston following the injury to Double Trigger's full-brother, Double Eclipse. The pair were expected to oppose each other at Ascot but Double Eclipse's recent foot injury brought home to Johnston how fortunate he would be to get one of the pair to the meeting.
"People don't realise how lucky you have to be to keep two top-class stayers sound and Double Eclipse's injury proved the point to me," he said.
Ashkalani, the favourite for the St James's Palace Stakes on Tuesday, worked well at Chantilly yesterday and his trainer, Alain de Royer-Dupre, confirmed that Michael Kinane will deputise for Gerald Mosse if the latter's appeal against a four-day ban is unsuccessful. Also Ascot bound is John Hammond's Prix Lupin third, Fort Nottingham, with the King Edward VII Stakes his target.Reuse content