KENNETT SQUARE, Pa. – Barbaro’s perilous road to recovery has suffered its biggest setback yet.

The Kentucky Derby winner faces major problems for the first time since surgery to repair the right hind leg he shattered in the Preakness seven weeks ago. And the colt’s veterinarian says “we’re in tough times right now.”

Barbaro had a new cast applied for a sixth time Monday – the fourth change in a week. The latest development followed three hours of surgery Saturday night when doctors replaced the titanium plate and many screws and also treated an infection.

“I think we’re in for tough times right now. I think we’re going to have some tough days ahead,” Dr. Dean Richardson said at the University of Pennsylvania’s New Bolton Center. “I’m being realistic about it. When a horse has a setback like this, it’s a problem.”

Richardson, the chief surgeon at the New Bolton Center, looked haggard during the briefing, and said it took more than 15 hours from the start of Saturday’s surgery until Barbaro had fully recovered from anesthesia.

“We went six weeks with nothing going wrong, essentially and one week where we’ve had things we’ve been dealing with,” Richardson said. “There’s no question this is a setback and we’re trying to address the problems.”

Last Monday, Barbaro had the cast on his injured leg replaced and three new screws inserted. On Wednesday, another new cast was applied after the horse showed discomfort. A small abscess on the sole of his left hind hoof also developed.

Richardson said Barbaro’s main fracture was healing well, but the pastern joint – located above the hoof which was shattered into more than 20 pieces – continues to be a concern. The joint, which doctors are attempting to fuse, was stabilized with “new implants and a fresh bone graft.”

The long cast applied Saturday night was replaced by a shorter cast Monday, and “was done with Barbaro in a sling and under mild sedation,” Richardson said.

Richardson said he never expected Barbaro to be in this situation a week ago because of what had been a smooth recovery. But a fever, a swollen pastern joint and the infection derailed the strapping 3-year-old colt’s recovery.

There’s reason for optimism, though, especially if Barbaro responds well to his latest surgery.

“If he stays comfortable, then I think we’re OK,” Richardson said. “If we can’t get him comfortable than it’s going to be a difficult problem.”

The infection developed in the leg in which the plate and 27 screws were inserted after Barbaro’s breakdown at Pimlico Race Course in Baltimore.

“It’s one of those setbacks that we’ve prepared ourselves for as best we can,” owner Gretchen Jackson said Monday. “Sure it’s disappointing, but we’ve been warned. … But a lot of bone has healed, a lot. There’s a lot of good stuff. And the horse is incredibly strong, healthy and we’ve got to keep the faith.”

Richardson said there was no reason to think that Barbaro’s life was in immediate jeopardy.

“We’re not at that stage, no,” Richardson said. “That never was even brought up as close to a topic of conversation. The issue is what’s the best thing for the horse.”

Barbaro won the Derby by 6 1/2 lengths, was unbeaten in six races and expected to make a Triple Crown bid before his misstep ended his racing career.