Russian boxer Maxim Dadashev has died at the age of 28.
Dadashev was fighting for his life with "severe brain damage" following his brutal defeat to Subriel Matias in Maryland last Friday.
Dadashev collapsed in front of fans as he made his way out of the arena at the MGM National Harbor after suffering a subdural haematoma, a bleed on the vein beneath the skull.
His condition is said to have deteriorated rapidly after arriving in hospital.
Boxing manager Egis Klimas claimed Dadashev underwent emergency surgery to have the right side of his skull removed in an attempt to reduce the brain swelling.
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But Russian outlet RT have reported the Russian has died in a hospital in the US - one day after Moscow celebrated its annual 'International Day of Boxing'
Dadashev has one son Daniel with his wife Elizabeth, with the family living in Oxnard, California.
The 28-year-old had won all 13 of his previous fights before the brutal defeat to Matias in the States.
He was also a silver and bronze medallist in the Russian championships before turning professional.
His trainer Buddy McGirt was forced to halt the 140-pound world title eliminator bout with Puerto Rican Matias after the 11th round.
Heart-breaking footage of the incident showed McGirt pleading with Dadashev to let him stop the fight.
The clip shows a weary Dadashev making his way to the corner when McGirt tells him: "I am going to stop the fight.
"Max, I am going to stop it. Please let me do this, you are getting hit too much."
Dadashev's passing is likely to lead to more calls to improve the safety of boxers in the ring moving forward.
British fighter Nick Blackwell was forced to retire in 2016 after he was placed in a medically-induced coma following his defeat to Chris Eubank Jr.
Matchroom chief Eddie Hearn led the tribute to the Russian, posting on Twitter: "So terribly sad to hear the news of the passing of Maxim Dadashev. Rest in peace."