HOT SPRINGS, Ark. (AP) – Rockport Harbor has a blood clot in his neck and may miss the Arkansas Derby, jeopardizing his chances to run in the Kentucky Derby on May 7.

John Servis, who also trained last year’s Kentucky Derby winner Smarty Jones, said Monday the baseball-size clot is dissolving and there’s a chance the colt could still make the Arkansas Derby on April 16.

Servis, though, nominated Rockport Harbor for the Lexington Stakes at Keeneland on April 23, calling it his “Plan B.” Servis said it’s possible Rockport Harbor could return to the Oaklawn Park track Wednesday.

Unbeaten in four starts last year, Rockport Harbor ran an admirable second to Greater Good in the Rebel Stakes on March 19 in his first race since last November. The effort kept him among the top-rated Derby contenders. Stewart Elliott, who rode Smarty Jones, also rides Rockport Harbor.

Since late last year, the gray colt has been fighting leg injuries, including an ailing right rear hoof, and had missed several days of training. The blood clot was discovered Saturday, and the 3-year-old missed his weekend workouts.

With the Kentucky Derby less than five weeks away, Servis is working against the clock to have owner Rick Porter’s colt ready.

“The Arkansas Derby is the ideal race, but I won’t know for a couple of days if he can make the race,” Servis said. “They accept late nominations for the Lexington, I guess for horses who are scrambling. And that’s us.”

“I need to have a Plan B in case Rocky can’t make the (Arkansas) Derby.”

Servis said Rockport Harbor’s blood clot was infected, but was not forming an abscess. “Otherwise, we’d be done.”

The trainer said Rockport Harbor was treated for 90 minutes Sunday by Dr. Douglas Byars, a Lexington, Ky.-based veterinarian.

“In time, he will make a complete recovery,” Servis said. “But time is not on our side. That’s for sure.”

Rockport Harbor was left with a gash on his right rear leg while winning the Remsen Stakes at Aqueduct on Nov. 27. He was given time off to fully recover, then missed eight days of training since late February with a bruised left front foot.

Servis planned on taking Rockport Harbor on the same Derby path as Smarty Jones. But injuries forced Rockport Harbor to miss the Southwest Stakes, and he was only “65 to 70 percent” healthy for the Rebel.

Smarty Jones won both of those races, then took the Arkansas Derby before nearly sweeping the Triple Crown, winning the Kentucky Derby and Preakness but finishing second by a length to Birdstone in the Belmont Stakes.