Castillo entered the ring to face light-heavyweight debutant Callum Smith, and the contest ended in shocking fashion.
After being knocked down by Smith, Castillo began to shake uncontrollably, before being stretched out to the back.
Matchroom Boxing promoter Eddie Hearn tweeted to confirm that Castillo was responsive and being sent to hospital, but the aftermath of the spectacular knockout reverberated around the arena.
The crowd, which had been fairly loud for the appearance of Smith, were extremely quiet following the initial hit and fall from Dominican Republic fighter.
Thankfully the fighter was responsive and taken to a medical facility about 10 minutes after the fight, but those ten minutes were extremely tense inside Tottenham Hotspur stadium.
What happened to Lenin Castillo?
Although the official medical report has not been released, it appeared as though Castillo suffered shock and potentially a seizure following the knockout blow from Smith.
Smith would talk to the press following the contest about the brutal nature of the knockout. He said: “That’s never nice to see, to be honest with you, especially when it’s you involved in it. It’s a sport at the end of the day and I was just hoping he left the ring safe.
“I’m hearing he’s responsive so fingers crossed everything’s okay, but it’s never nice to see. I wanted to win but you never want to win in that way.”
Smith had begun celebrating following the knockout, jumping onto the rope after the knockdown. After realising what had happened, Smith cut his celebrations short in concern over this opponent's health.
Despite the scare, this was Smith’s first contest after losing to Canelo Alvarez at super-middleweight back in December, so it was an impressive return for the Brit.
There is currently no update on the condition of Castillo, although we hope to hear about his status in the coming days.
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