Gracida, 53, died Tuesday after never regaining consciousness, the Palm Beach (Fla.) Post reported.
He was injured while playing in the International Polo Club's Freebooters Classic 14-goal Tournament at Everglades Polo Club in Wellington. His horse was accidentally hit in the head by another player's mallet. The stunned horse hit Gracida in the head, knocking him unconscious. Gracida fell to the ground and the horse rolled on top.
Gracida died late Tuesday night at a hospital in Delray Beach. He reportedly suffered bleeding and swelling of the brain.
Born in Mexico, Gracida was a resident of Wellington, Fla. He won the U.S. Open nine times and the Argentine Open five times. He was named Player of the Year five times, earning the highest rankings in polo in 1985.
Gracida maintained his 10-goal ranking for 15 years.