Buick had ridden the Mark Johnston-trained Permian to finish last in the Grade One Secretariat Stakes when the colt fractured a foreleg and unseated the rider shortly after crossing the line.
Permian had to be put down due to his injury while Johnston's son and assistant, Charlie, reported Buick had been taken to Northwest Community Hospital "complaining of back pain".
It was later reported by the Daily Racing Form he had suffered a fractured T12 vertebra, but would require no surgery. Buick is set to see a specialist on Tuesday, when more will be known about how long he may be on the sidelines for.
Buick's father, Walter, issued an upbeat bulletin early on Sunday, saying: "It could have been an awful lot worse. I've spoken to him and he is in good spirits."
Buick is number one rider to Godolphin trainer Charlie Appleby, who had said on Sunday afternoon: "He's due to be looked at again and is hoping to be home in the next 24 hours."