UFC star Derrick Lewis has revealed CCTV footage of him knocking out a boxer who allegedly talked trash to him.

Lewis, who is one of the hardest hitting heavyweights in the UFC, reportedly took on a boxer at his gym who claimed that he could knock Lewis out – and it didn't turn out well for the trash talker.

The footage, which Lewis tweeted, shows the the 34-year-old fighter laying into his opponent with a barrage of blows in a boxing ring before the boxer eventually goes down.

"When a boxers [sic] said he will knock me out because I'm an MMA fighter," Lewis wrote in the tweet.

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In another post on Instagram, Lewis said: "When a boxer comes to my gym talking s*** … HE'S OK."

UFC heavyweight Derrick Lewis taking on a boxer in the ring. Photo / Twitter
UFC heavyweight Derrick Lewis taking on a boxer in the ring. Photo / Twitter

According to ESPN's MMA journalist Ariel Helwani, the fight only lasted one minute.

"Asked Derrick about this," Helwani said in a tweet. "He said a boxer at his gym was talking "a lot" of smack about boxers vs MMA fighters. This happened yesterday. Lasted 1 minute, he said."

MMA fans were quick to praise video, but some weren't happy that Lewis continued to punch his opponent while he was down.

"Few dirty digs when he was out cold," said one fan.

Lewis, who lost to Kiwi Mark Hunt in Auckland two years ago, has a record of 22 wins (18 knockouts) and seven losses.