Russian boxer Maxim Dadashev has died following injuries suffered in his IBF light-welterweight fight against Subriel Matias in Washington on Friday.
The bout was stopped by Dadashev's trainer Buddy McGirt at the end of the 11th round and the 28-year-old was taken to hospital with bleeding on the brain but failed to recover following emergency surgery.
A statement from the Russian Boxing Federation said: "Russian boxer Maxim Dadashev died in the United States as a result of injuries suffered in a fight with Subriel Matias. The Russian Boxing Federation expresses deep condolences to Maxim's family and friends."
Dadashev had won all 13 of his previous fights before the match with Puerto Rican Matias and, after receiving heavy punishment in the latter rounds, McGirt called a halt to proceedings at the MGM National Harbor, but the fighter failed to wake up from a medically-induced coma.
"It just makes you realize what type of sport we're in, man," McGirt told ESPN.
"He did everything right in training, no problems, no nothing. My mind is like really running crazy right now. Like, what could I have done differently? But at the end of the day, everything was fine (in training).
"He seemed OK, he was ready, but it's the sport that we're in. It just takes one punch, man."
Dadashev's promoters Top Rank paid tribute to Dadashev, saying on Twitter: "Maxim was a talented fighter inside the ring and a loving husband and father outside the ropes. Our thoughts and prayers are with his family and friends."
Former featherweight world champion Carl Frampton tweeted: "Saddened to hear about the passing of Maxim Dadashev. Deepest condolences to his friends and family. RIP."
Promoter Eddie Hearn added: "So terribly sad to hear the news of the passing of Maxim Dadashev. Rest in peace."