Japan's leading sire, Sunday Silence, is suffering from laminitis, a debilitating disease of the hoof, and may be euthanized within the week.

The news broke Friday, shocking and saddening racing fans worldwide. The American champion, who stands at Shadai Stallion Station in Hokkaido's Hayakita, recently underwent three operations for an infection on his right foreleg.

Shortly after the third operation on July 18, Sunday Silence began showing signs of laminitis in his left forelimb and his condition gradually worsened.

Eisuke Tokutake, a spokesman for the Shadai operation, said Friday that the stallion, though eating and still able to stand by himself, appears to be in considerable pain.

"He's such a strong horse mentally that I don't think it shows how much he's suffering, but I think he's really fighting," Tokutake said.

The 16-year-old Sunday Silence, by Halo, out of Wishing Well, first captured hearts with his renowned rivalry with 2-year-old champion Easy Goer in the American 1989 classics.

Sunday Silence beat Easy Goer in the Kentucky Derby and Preakness, but lost to him in the Belmont.

He went on to win the Breeders Cup Classic that year and was named champion 3-year-old and Horse of the Year.

Sunday Silence began stud duty in Japan in 1991 and has changed the face of Japanese racing. He has been the country's leading sire at the national level for the past eight years and currently has 328 offspring running in Japan Racing Association-sponsored races.