Man’s Best Friend has been ruled out of the £740,000 race at Keeneland on Friday while Great Barrier Reef followed him out of the Juvenile Turf when examined on Friday. Ryan Moore has switched to Haffner

Aidan O’Brien’s formidable team of two-year-olds running at the Breeders’ Cup at Keeneland on Friday has been depleted.

The Ballydoyle trainer declared four horses in the £740,000 Juvenile Turf but by the time of the race that number will have been halved.

Man’s Best Friend, the winner of the Richmond Stakes at Glorious Goodwood over the summer who was due to be ridden by Colin Keane, was scratched early Friday morning. Then Ballydoyle's number one hope in the race, Great Barrier Reef, the mount of Ryan Moore who finished third in the Dewhurst Stakes last time out, was ruled out later, both officially declared as "unsound", leaving O'Brien with Haffner and Florida Bay.

O’Brien has won the last four runnings of the Juvenile Turf but the trainer revealed on Thursday that Great Barrier Reef was being treated for a stone bruise. Haffner and Florida Bay are the trainer’s remaining runners.

He was set to be reassessed on Friday but O’Brien conceded: “It’s very possible he could come out.”

Every runner at the Breeders’ Cup has to undergo enhanced veterinary checks which often results in late withdrawals.

One big name from the American team was ruled out on Thursday when the Dubai World Cup winner Magnitude, one of the leading candidates for the Classic, was scratched under veterinary advice.

He was immediately retired to Coolmore-owned Ashford Stud, leaving just seven horses to go to post on Saturday, headed by Japan’s defending champion Forever Young, and reigning US Horse of the Year, Sovereignty.

Magnitude’s trainer Steve Asmussen told Daily Racing Form : “A PET scan revealed some disruption in the suspensory fibres of his left foreleg, and after discussions with [Winchell Thoroughbreds’s] Ron Winchell and David Fiske, it was decided to err on the side of caution and not take any risk with a tremendous horse.

“We're nothing short of heartbroken because of how well we expected him to run.”