Harbinger has been hailed as "one of the all-time greats" after injury forced connections to announce the colt's retirement from racing.

The four-year-old colt became the highest-rated Flat horse in the world following his breathtaking 11-length triumph in last month's King George VI And Queen Elizabeth Stakes at Ascot.

But less than a fortnight before his next intended target, the Juddmonte International at York on August 17, Harbinger fractured his near-fore cannon bone on the gallops in Newmarket on Saturday.

The son of Dansili underwent surgery on Saturday evening, but connections felt it was too much of a risk to return the Sir Michael Stoute inmate to the racecourse.

A decision on a potential stud career has yet to be confirmed.

Harry Herbert, racing manager for Highclere Thoroughbred Racing, said in a statement issued on behalf of the colt's owners, the Admiral Rous Syndicate: "It is with regret that it has been decided to retire Harbinger from racing.

"Thanks to the professionalism of the veterinary surgeons, Bruce Bladon of O'Gorman Slater & Main, Andrew Bathe of Rossdale & Partners and Antony Clements of Baker & McVeigh, the operation undertaken at Rossdales Hospital has been successful.

"We are pleased to report that the horse is recovering well. The decision to retire Harbinger is based on the welfare of the horse which is paramount. The owners, for whom this is very sad, are naturally sorry that their great horse has had his career cut short.

"In winning the Hardwicke Stakes so impressively and then producing one of the greatest performances of all time to win the King George VI and Queen Elizabeth Stakes by 11 lengths in record time, Harbinger has confirmed himself as one of the all-time greats."