Russian boxer Maxim Dadashev has died at the age of 28 following injuries suffered in his IBF light-welterweight fight against Subriel Matias.
Dadashev was reportedly unable to walk to the dressing room after his bout was stopped by trainer Buddy McGirt at the end of the 11th round on Friday.
He was hospitalised with bleeding on the brain and underwent emergency surgery but failed to recover.
The Russian Boxing Federation says it has opened an investigation.
Secretary general Umar Kremlev suggested there was "some kind of violation", adding in a statement: "We lost Maxim Dadashev. He was our young prospect.