Trainer Bob Baffert said the gray colt is expected to recover after surgery on his right knee.
Flashback goes to the bench with two wins and two seconds from four starts. His injury leaves Baffert, a three-time Derby winner, without a first-line contender for the May 4 Run for the Roses.
Among Baffert's other 3-year-olds, Governor Charlie stands 10th on the points list toward a Derby start thanks to his win in the Sunland Derby in New Mexico. Den's Legacy is No. 19 and in danger of being bumped unless he runs well in Saturday's Arkansas Derby. Baffert also is expected to saddle War Academy in Arkansas but he would need a first- or second-place finish to get in the Louisville starting gate.