Age Of Aquarius's leg injury at Goodwood on Thursday could presage the end of his career as a racehorse.
Aidan O'Brien's charge broke down with around half a mile to run of the Artemis Goodwood Cup.
It was later confirmed that the four-year-old had sustained ruptured ligaments below the fetlock of his off-fore.
Dr Paul Dupreez, senior partner of the Arundel Equine Hospital, said: "He is fine and is on his way home, supported by a splint and bandages.
"It is not a catastrophic injury, but there are huge doubts as to whether he will be able to get back to competitive action.
"He's a very valuable horse and I'm sure they will have plans for him."
Jockey Johnny Murtagh said: "He was travelling OK, but lost his balance for a couple of strides and it went pop. It was disappointing as he was going well."
Age Of Aquarius went off as favourite for the Goodwood Cup, which was eventually won by Illustrious Blue.