Jockey Norbert Arroyo Jr. was injured in a spill during the first race Saturday at Aqueduct.
Dr. Marie Jacques said Arroyo had possible rib fractures and was "in excruciating pain."
Arroyo was taken to Jamaica Hospital for further examination. He later sought another opinion at North Shore University Hospital, where he was listed in stable condition.
Arroyo was injured when his mount, Pete Shure, clipped heels with Fast Modem and fell after entering the stretch. Cryptoe Tap, ridden by Lorenzo Lezcano, also fell. Lezcano and both horses escaped injury. According to Equibase charts, Proud Marine jumped a fallen horse and went on to finish sixth, 23 lengths behind fifth-place Max Patch, who had been steadied to avoid the spill. Max Patch came home 15 lengths behind fourth-place finisher Rock Layer in the claiming race won by 9-5 favorite Speedway Sport.