Harbinger is reported to be in a comfortable condition following surgery after suffering a career-threatening leg injury.
The brilliant winner of the King George VI And Queen Elizabeth Stakes, owned by Highclere Thoroughbred Racing, fractured his near-fore cannon bone during a routine spin on the gallops in Newmarket.
"He had a comfortable night. The surgery he had was straight forward and all of those things," said John Warren, co-owner of Highclere Stud.
"Hopefully we will know more later this afternoon."
Harbinger, trained by Sir Michael Stoute, was officially rated the best horse in the world when winning the King George by 11 lengths in a record time.
He was next scheduled to run in the Juddmonte International at York later this month, after which the Prix de l'Arc de Triomphe was on the agenda.
The son of Dansili has won his last four races, including the Hardwicke Stakes at Royal Ascot, and has accrued over £770,000 in prize-money.
