Luke Nolen has been taken to hospital in Adelaide, conscious but in pain, after a fall in the Group One Robert Sangster Stakes in Adelaide.
Australian Jockeys' Association representative Des O'Keeffe said Nolen was conscious and moving his arms and legs but complaining of back pain.
Nolen, best known as Black Caviar's regular jockey, only returned to riding in February after a long lay-off as he recovered from back surgery.
The incident happened just 40 minutes after Nolen won the other Group One race at Morphettville on Saturday, the Australasian Oaks on the Mick Kent-trained Abbey Marie.
He came off Miss Promiscuity early in the Sangster won by Precious Gem, ridden by Jake Noonan.