One of two Bob Baffert-trained entries in the derby, along with Authentic, Thousand Words was seen as a contender with 10-1 odds at the time he was scratched.
NBC announced a veterinarian at Churchill Downs made the decision to remove the bay colt from competition after he hit his head during the fall. Thousand Words is the fourth entry in the derby scratched this year following Art Collector, King Guillermo and Finnick The Fierce.
The incident left Baffert's longtime assistant, Jimmy Barnes, with a broken arm that required him to leave Churchill Downs in an ambulance at the same time Baffert's second Derby entry, Authentic, was crossing the finish line to win the Run for the Roses.
Pat Forde of Sports Illustrated reports Thousand Words was checked out and cleared by the track vets and is "absolutely fine".
Thousand Words had a strong season heading into the derby, winning at Del Mar and twice at Santa Anita while claiming four first-place finished dating back to last October. In its last two races, the colt finished first and second after an uncharacteristic stumble at the Oaklawn Stakes in April.
Baffert won his sixth Kentucky Derby on Saturday with Authentic after previously finding success with Silver Charm, Real Quiet, War Emblem, American Pharoah and Justify. The 67-year-old has tied Ben Jones record for most Kentucky Derby wins by a trained and has set the record for most Triple Crown races with 16.
Thousand Words' exit left just 15 horses in the field for Saturday's race.