Last updated on .From the section Boxing

Boxer Curtis Harper has been criticised by his trainer for leaving the ring after the opening bell of a heavyweight bout in protest over pay.

The 30-year-old American instantly walked out of the arena when the bell sounded for his bout against Efe Ajagba of Nigeria in Minneapolis.

Trainer Nate Campbell said he was "embarrassed" by his fighter's move.

"This man disrespected himself, his wife, the fans and me," Campbell posted on social media.

Journalist Jordan Hardy - who works for Premier Boxing Champions, which was broadcasting the fight - said Harper told her the walkout was because of money.

"He walked out of the ring because he's not getting paid enough to fight and that he wants respect," she wrote on social media.

'Why did he take the deal?'

Promoter Leon Margules told BBC Sport organisers had no idea of Harper's plan before the bout and confirmed the fighter received no payment as a result.

"He signed a contract and agreed to the fight," said Margules. "First time we heard about money issues was after he left the ring. He weighed in and showed up on time and even touched gloves before the bell. It is strange.

"If he didn't like the deal, why did he accept the fight and money?"

Harper had reached the bottom of the steps at the side of the ring with just five seconds gone in the round.

Fans began booing as he made his way along the walkway out of the ring and officials disqualified him at the one-second mark of the first round.

Britain's former unified heavyweight champion of the world Lennox Lewis shared footage of the incident on social media.

Writing on Twitter, Dave Coldwell, trainer of British heavyweight Tony Bellew, said: "Boxing...expect the unexpected!! Can't say I've ever seen this before!"

Harper now holds a record of six defeats and 13 wins, while Ajagba, 24, has six wins from six, including five knockouts.

How do you commentate on one second?

Host broadcasters Premier Boxing Champions were as surprised as those in attendance at the Minneapolis Armory when Harper made his exit.

Commentator one: "Do not blink. Of Ajagba's five professional bouts, four have been done in the first round - so he likes to bring an end to opponents in quick fashion."

Bell rings

Commentator one: "And Curtis Harper has walked out of the ring."

Commentator two: "Wait, what? I have never seen this before. He has walked out of the ring. He's not fighting this guy. I have never seen this before in my life and the fans are really upset right now."