"Maxim Dadishev died in the United States after injuries that had been halted during his struggle with subrule maths," the report said.
The super-heavyweight (up to 63.5kg) Russian-Puerto Rican fight was stopped in 11th by the James McDit of Dadashev.
Dadashev, 28, who was nicknamed "Crazy Max," couldn't go to the locker room after the fight and was taken to hospital immediately.
In Washington, doctors underwent surgery to relieve the swollen brain.
"At the moment, his condition is critical, but the doctor told me he is a stool," Donatas Januševičius, a Lithuanian fitness trainer, told Dadeshev after the operation.
Mr. McGirt said after the fight, he could "not persuade" his fighter to stop, but decided to throw in the towel when he saw "as he continues the fight he misses more and more kicks."
The video of Buddy McGirt, who asked Maxim Dadashev to keep fighting, was hard to watch Friday, even harder now. Heart-breaking. pic.twitter.com/BNjsdpJfle
– Ariel Helwani (@arielhelwani) 23 2019 July 2019
"A single shot can change a guy's life," the second person stressed.
The Russian boxer Umar Kremlyov said for media in his country that Dadshevik's body will be repatriated and that his family will receive financial support.
Dadashev won all 13 of his fights in the professional boxing ring, but no title was sought.
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