Rio King, who was claimed for $20,000 from a maiden race last October and was second in the Grade 3 San Francisco Mile at Golden Gate Fields in April, was euthanized earlier this month because of a spinal injury that caused hind end paralysis.
Trainer Samuel Calvario said on Wednesday that Rio King was found stricken in his stall at Pleasanton. After treatment and veterinary consultation, it was determined that Rio King could not be saved.
The cause of the injury was not known, Calvario said.