There were scary scenes on the Anthony Joshua vs Oleksandr Usyk undercard on Saturday evening.
Callum Smith returned to the ring at the Tottenham Hotspur Stadium as he made his light-heavyweight debut.
His opponent was Dominican fighter, Lenin Castillo.
The fight came to a premature end in the second round when Smith caught his opponent square on the chin.
Castillo collapsed backwards and began shaking on the floor. The referee immediately waved off the fight.
The 33-year-old had to be stretchered off and has been taken to hospital.
Fortunately, Castillo has only been taken to hospital for precautionary measures.
Citing Sky Sports, talkSPORT journalist Michael Benson wrote on Twitter: "Sky add that he's conscious and just going to hospital for precautionary measures."
Eddie Hearn has also tweeted after the knockout.
He wrote: "A horrible brutal knockout. Castillo is responsive and on his way to hospital."
We wish Castillo all the best and a speedy recovery.