Among the many requirements for those in the Thoroughbred industry is the ability to steel oneself against the highs and lows of the sport.

For the connections of champion Animal Kingdom, Sunday was one of those times that tested their reserve.

Team Valor's Animal Kingdom, winner of the 2011 Kentucky Derby, will not make his expected start in the $10 million Dubai World Cup on March 31 after emerging from his recent workout with an injury to his left hind leg, it was announced Monday.

In his first move since winning an allowance race on the turf at Gulfstream Park on Feb. 18, Animal Kingdom breezed 5 furlongs in 1:04.80 over the turf at Palm Meadows Training Center on Saturday. The following morning, trainer Graham Motion said the son of Leroidesanimaux was lame in his left hind.

Animal Kingdom had surgery to repair a hairline fracture of his left hock following his sixth-place finish in the Belmont Stakes in June, but Motion said the nature and severity of his current injury is still being determined.

"We really don't know what it is right now," Motion said. "There is nothing obvious apart from the fact that this is the same leg that he injured before. Obviously when you have an injury like that, arthritic changes come with that but ... the site (of the previous injury) looks very good.

"More than likely he'll go for a bone scan in the next 48 hours to figure out what is going on. It could be something completely different, it just happens to be on the same leg. We don't really know at this point."

Motion and Team Valor could still be Dubai bound, however, as stakes winner Lucky Chappy is likely to be among the entrants for the $2 million UAE Derby on the World Cup undercard.

Adding to the dismay surrounding Animal Kingdom's injury is how well he seemed to recover from his previous setback.

In his first start since the Belmont Stakes, the 4-year-old chestnut colt easily beat five others in his 11⁄16-mile comeback race, winning by 2 lengths under jockey John Velazquez.

Considering Animal Kingdom won the Grade III Vinery Racing Spiral Stakes on the Polytrack at Turfway Park last March, he was considered a strong contender for the Dubai World Cup, which is also contested over a synthetic surface.

"This is a crushing blow for our company and our partners as well as our trainer, who has done such a great job getting the horse back to this point," Barry Irwin, CEO of Team Valor, said in a statement. "If he comes out of this okay, hopefully we can run in the World Cup in 2013."

Animal Kingdom's ailment cast a pall over what should have been a stellar Sunday for Motion, Velazquez and Team Valor. Hours after the reigning 3-year-old champion male was found to be lame, his stablemate Howe Great — also owned by Team Valor and ridden by Velazquez — defeated Grade I winner Dullahan in the Grade III Palm Beach Stakes at Gulfstream Park.

"To go from the morning watching (Animal Kingdom) walking in the barns to saddling that horse (Howe Great) in the afternoon, that's about as extreme as you can get," Motion said. "I think to come this far and to get this close and have the prep go so well, it's pretty tough."

Fed Biz out of Derby

Promising allowance winner Fed Biz has been declared off the Kentucky Derby trail with a hind-end issue, trainer Bob Baffert told Daily Racing Form on Monday. Fed Biz was slated to run in the Grade II San Felipe Stakes this past Saturday, but he wasn't entered in the race when the issue developed earlier in the week.

"I'm taking him off the Derby trail," Baffert told Daily Racing Form. "I took him back to the track, and he's still not comfortable. I'm going to stop on him. He's got a hind-end issue. We can't find it, but something's nagging him. I'm going to give him some time off."

Alicia Wincze Hughes: (859) 231-1676. Blog: horseracing.bloginky.com.