Sir Michael Stoute believes Harbinger had the potential to become the undisputed best horse in the world by the end of the season.

The legendary trainer was making his first public comments since the colt, already the top-ranked performer on international ratings, fractured his near-fore cannon bone in a routine piece of work on the gallops on Saturday.

Asked how much further Harbinger could have gone, he said: "Who knows? If he had kept at that plateau, we'd have a world champion."

Harbinger, who is owned by Highclere Thoroughbred Racing, had been considered for next week's Juddmonte International at York but was officially retired on Monday.

His career reached a dazzling peak in his final run, when demolishing his rivals in the King George VI and Queen Elizabeth Stakes at Ascot.

Stoute added: "It was a big blow for all concerned with the horse. He was a nice character and he proved in the King George how good he had become. The Hardwicke was a hint to how he was progressing to the top and the King George confirmed it.

"You've just got to keep cool and remember there are people suffering more than you, like the girl who looks after him and the girl who rides him.

"He has come through the surgery well and it wasn't a complicated fracture. There are 12 owners and they had to make that decision (to retire)."