American boxer Leavander Johnson died on Thursday from injuries sustained five days earlier in a lightweight title fight with Jesus Chavez.
The 35-year-old's kidneys had failed and his heart was not pumping on its own when family members decided to remove him from life support, his doctor said.
"We had no further mode to improve his prognosis, so the family very correctly made the decision to withdraw care," Dr. William Smith said. "He passed away very peacefully."
Johnson collapsed on his way to the dressing room after taking a beating in his IBF lightweight title defense on Saturday. Doctors were operating on him within 40 minutes to relieve pressure on his brain, but he never came out of a medically induced coma.
Smith said he performed a second operation on Monday to remove a blood clot but Johnson was too gravely injured to survive.
"He suffered a very severe injury. The problem is that the injury was to the brain itself," Smith said. "In some cases, the punishment is absorbed by the skull, but in this young man's case, the brain absorbed the punishment itself."
Johnson's promoter, Lou DiBella, said Johnson's family members were present when he died. Johnson's father was his trainer and his brother was his manager.
"What a wonderful guy this was. And I've never met anybody so proud or so grateful to achieve his dream," DiBella said. "If there's any solace to be taken in this, it's that he died doing what he loved. He died a champion."
Doctors were initially unsure Johnson would make it through the night after being injured during the fight at the MGM Grand hotel-casino, but the next day Smith expressed cautious optimism after tests showed improvement in brain function.
Johnson spent 16 years as a professional fighter before finally winning a version of the 60kg title in June. But, in his first defense, he took a beating from Chavez before finally being stopped by a flurry of punches in the 11th round.
He walked from the ring, but on the way to the dressing room began showing signs of an injury. He was rushed to University Medical Center where Smith operated on him to relieve pressure from a subdural hematoma, or bleeding on the brain.
"There'll be a lot of people who'll take pokes at boxing for this. We can be better for protecting our athletes. But this was not a situation where anyone failed Leavander Johnson," said DiBella, who knew Johnson for more than 10 years. "It was just God's will. It's a sport that's inherently dangerous."
DiBella said Johnson's father, Bill, said Chavez was "blameless in this tragic situation." Chavez visited Johnson in the hospital the day after the fight.
Smith said it was not clear whether one punch or an accumulation of punches in the fight caused a swelling so pronounced that it pushed Johnson's brain from the right side of his skull to the left.