The decision to remove Sterling Racing's entrant from the May 4 classic at 1 1/4 miles was due to a non-displaced chip in a left ankle discovered after Black Onyx trained the morning of May 3, trainer Kelly Breen said.
"We noticed a little swelling in his ankle this morning," Breen said at a press conference at Churchill Downs. "It brought major concern right away. He did gallop this morning. He came back and on a scale of lameness on a one to five, it was a one. It did warrant us to take an X-ray where we found that he does have a chip in his left ankle."
The scratch came after the 9 a.m. scratch time. Also-eligible Fear the Kitten was scratched from the Derby earlier Friday morning.
"We started working with this horse early," Breen said of the timeline. "The time allowed to train this morning was 5:45 a.m., so I got to the barn at 5:15. Seeing what I saw, I knew we were behind the eight ball. This happens in racing often enough to say, 'this is bad timing' but he trained and actually looked pretty good training and I thought that, maybe like everyone else can do, he was having a bad day. The filling after he was done training warranted the X-rays that resulted in the finding of the non-displaced chip."
According to Breen, a first set of X-rays taken on the Rock Hard Ten colt around 9:30 a.m. did not detect the chip, but a second set found the minor injury.
"He's an athlete. He's been a sound racehorse and the filling that was there was something... it was significant enough to say this is not your average ache or pain,' Breen said. "That's why we went to X-ray right away. This was the first time we'd taken a X-ray of him."
Black Onyx was scheduled to break from the inside post in the Derby. Stewards have decided that the No. 1 slot will be left open in the Derby starting gate and the remaining 19 horses in the Derby field will start from the post positions they drew May 1.
"There was a thought to wait until tomorrow to see how he was," Breen said. "It was up to our discretion to take the X-rays. We wanted to find out what was going on. It could have been anything. If we could have helped him recuperate in a timely manner, it was up to us."
"Kelly's whole team has done so much and this shows that it's so tough just to get here," said jockey Joe Bravo, who accompanied Breen to the press conference. "Everybody loves these horses and they do get the best care. I worked this horse the last two times. The horse has so much heart he never showed me a sign of anything being wrong."
As for Black Onyx's future, Breen and Sterling Racing's Sam Herzberg are waiting.
"I spoke to Mr. Herzberg and saw him personally at the hotel," Breen said. "It's not the easiest of conversations to have when you first know something has gone awry. He still has a real nice racehorse."
"Our regular surgeon is Dr. (Larry) Bramlage and I believe he is still in the hospital. Dr. Foster Northrup is my attending veterinarian. He's put out a couple of feelers to some other surgeons. Dr. Tom Brokken is down in Miami and he's on the case. We should have a prognosis by the end of the day to see if it is routine surgery or time will heal the injury. We're waiting on some phone calls."
Bramlage was hospitalized May 2 after falling from a golf cart while in the Churchill stable area.
Evan Hammonds contributed to this article.