Chris Eubank Jr. claimed the British middleweight title with Nick Blackwell taken to hospital for further checks after a 10th round stoppage.
The referee called the fight off at London's Wembley Arena following advice from the doctor, with Blackwell unable to carry on due to large swelling over his left eye.
Blackwell was then taken from the ring on a stretcher with Hughie Fury's heavyweight fight against Dominic Guinn delayed.
The BBC has since reported that Blackwell has been placed in an induced coma, having suffered a bleed on the brain during the bout.
"I was hitting him with some hellacious shots. The referee saw fit to let the fight go on, maybe he should've stopped it earlier," Eubank Jr. told Channel 5.
"As you saw, he was taken out on a stretcher. This is boxing. He made a decision. It was a great fight.
"He was a hell of a competitor. This is what Britsh boxing needs, two warriors coming together. I wanted his belt, I've always dreamed of becoming British champion, and tonight it became a reality.
"I've been working my whole career towards this. Now that will lead onto bigger and better things. I want a world title shot."
Eubank Jr. dominated the contest and left his opponent's nose bloodied in the early rounds with a flurry of jabs and uppercuts.
Billy Joe Saunders, who handed Eubank Jr. his only defeat, was supporting Blackwell from ringside, with the challenger pointing a glove in his direction in round five after unloading an impressive combination.
Eubank Jr immediately caught a right from Blackwell after allowing himself to be distracted, but regained his composure to stay on top over the next three rounds.
Blackwell continued to withstand Eubank Jr.'s onslaught with round nine a quieter affair, but the referee finally stepped in and called the doctor over in the 10th round.
Chris Eubank Sr., the former world champion in his son's corner, felt the fight should have been stopped earlier.
"I'm not the referee," he told Channel 5. "I know how hard Junior hits. I know he's a very dangerous man. It happens. But I can't criticise anyone. Nick Blackwell has magnificent heart.
"The ref said to stop banging on the apron. I did shout they should stop the fight. It's not my place to say that. He had a job to do. He did it. The best man won."