"He spiked a temperature during the day on Tuesday," said trainer J.J. Toner, "and simply collapsed early in the morning. We are all incomplete shock over this turn of events."
An autopsy will be performed at the New Bolton Clinic of the University of Pennsylvania, the same place where Barbaro was sent after his 2006 Preakness Stakes injury.
Sailor's Cap, ridden by Alan Garcia, won Sunday's $100,000 Poker Stakes at Belmont. The four-year-old covered the one-mile turf race in 1:36.50 in defeating 3-5 favorite Kip Deville.
The colt was the winner of four of 10 lifetime starts for $616,970. Last year he won the $600,000 Colonial Turf Cup Gr.3 at Colonial Downs (in a downpour) and was third in the track's $700,000 Virginia Derby Gr.2.
"He was just coming into his own," said Team Valor president Barry Irwin. "This shows the highs and lows of this game. It is a tough nut to swallow."