Dean Richardson, the chief surgeon who has been treating Barbaro since the colt suffered catastrophic injuries in the Preakness on May 20, said the Derby winner's chances of survival are poor.
"I'd be lying if I said anything other than poor," Richardson said Thursday at a news conference at the University of Pennsylvania's New Bolton Center. "As long as the horse is not suffering, we're going to continue to try (to save him).
"If we can keep him comfortable, we think it's worth the effort."
If not, Barbaro could be euthanized at any time. Richardson said if Barbaro does not respond quickly to treatment, "It could happen within 24 hours."
Richardson said the laminitis nearly has destroyed the colt's hoof on his uninjured left hind leg. Laminitis, a painful condition, developed in the past few days. The disease turned more serious in the past day.
"The left hind is basically as bad laminitis as you can have," Richardson said, adding that horses have recovered from laminitis. He said he has discussed the situation closely with owners Roy and Gretchen Jackson.
Richardson said Barbaro's injured right hind leg, the one that shattered at the start of the Preakness, is healing well, but because a horse has to be evenly balanced, laminitis set in on the other foot.
"We removed a large portion of his (left) foot wall, probably 20 percent of it," Richardson said. "He's in a foot cast with foam padding and antiseptic dressing. We'll see if can regrow his hoof. It will take months and months."
The grim update came after nearly six weeks of a smooth recovery. Barbaro had hours of surgery on May 21 to insert a titanium plate and 27 screws into three broken bones and the pastern joint, and has had two other operations in recent days.
"I really thought we were going to make it two weeks ago," Richardson said. "Today I'm not as confident."
Barbaro's recovery had been going smoothly until the recent series of setbacks.
Owner Roy Jackson said the sudden changes in Barbaro's condition made this a tough week.
"We've been concerned all along," Jackson said Wednesday. "It's just one of those things. It's very difficult to climb the mountain when something like that happened."