Kafwain and jockey Victor Espinoza following the San Vincente.

The preliminary diagnosis was that Kafwain suffered an injury to the check ligament of his right foreleg, according to Richard Mulhall, the racing manager of The Thoroughbred Corp.

"It just happened today," Mulhall said. "He had been perfect. It looks like there is a little filling there."

Kafwain worked five furlongs in 59.60 seconds.

"We noticed he was just a tad off," trainer Bob Baffert said. "I didn't look bad but with this thing, you can't chance it."

A winner of four of 11 starts and $715,848, Kafwain was considered an outsider for the Kentucky Derby. A two-time stakes winner last year and the runner-up in the Breeders' Cup Juvenile at Arlington Park, Kafwain had one win in three starts this year. He scored a convincing win in the San Vicente Stakes at Santa Anita on Feb. 1, but was second in the Louisiana Derby (later disqualified from the prize money because of a positive test) and third in the Santa Anita Derby.

Since that race, Kafwain missed a week of training because of illness, but had been training steadily for the last two weeks.

The absence of Kafwain will prevent The Thoroughbred Corp. from attempting to become the first owners since Meadow Stable (1972-73) to repeat as winners of the Kentucky Derby.

Baffert spoke glowingly of the workout from Indian Express . He described the move as "the best he's ever worked." Ridden in the workout by exercise rider Dana Barnes, Indian Express broke off in front of Kafwain, while racing along the rail.

Indian Express finished second in the Santa Anita Derby at 35-1, his first start in a Grade 1. After leading on the final turn, he finished a head behind Kentucky Derby hopeful Buddy Gil.

Senor Swinger has been considered a candidate for the Kentucky Derby, but was entered for Friday's $100,000 Crown Royal American Turf for 3-year-olds over 1 1-16 miles, Baffert said. He finished fifth, beaten 9 1-4 lengths, in the Wood Memorial, his first start for owners Bob and Beverly Lewis and Baffert.

Senor Swinger galloped on Tuesday.

Domestic Dispute galloped 1 1-2 miles on Tuesday. California owners David Bienstock and Chuck Winner purchased Domestic Dispute from Baffert's stable last weekend.

New trainer Paddy Gallagher is contemplating giving Domestic Dispute a minor workout later this week.

"I don't know whether to breeze him or not," he said. "I should probably blow him out."

Outta Here had his first exercise at Churchill Downs on Tuesday with a gallop. He arrived from California at midday on Sunday and walked on Monday. Outta Here has made one start this year, finishing fourth in the $2 million United Arab Emirates Derby in Dubai.

Buddy Gil only walked at the barn on Tuesday, having worked on Monday. Trainer Jeff Mullins said that Buddy Gil would gallop for the rest of the week, with a schooling session in the starting gate and the paddock scheduled for later in the week.