Floyd Mayweather still trains "like he's going to fight one of the top welterweights", says Devin Haney.
Mayweather retired in 2017 after extending his record to an unbeaten 50-0 against Conor McGregor, although he has since won an exhibition bout against Tenshin Nasukawa, and plans another against YouTuber Logan Paul.
Now 43 and the winner of boxing's two richest fights ever, against Manny Pacquiao and McGregor, Mayweather has retained the work ethic that has made him a modern boxing great according to Haney.
"His work ethic is crazy because he is still working. He still gets up at 5 or 6am to go running," Haney told Sky Sports.
"He is training in the gym. He works like he's going to fight one of the top welterweights today."
Undefeated WBC lightweight champion Haney and his divisional rival Gervonta Davis have both spent time training under Mayweather's watch.
"It's great," said Haney. "I'm thankful to spend time and to learn from the Michael Jordan of boxing.
"He is a guy who has accomplished the most in his era, and someone I can learn so much from."
Haney insists that Mayweather's brash personality and his 'Money' moniker are only a public perception.
"He is different when you get to know him, and when you spend time with him," said Haney.
"I wouldn't say more humble because I don't feel like he is cocky - he just does what he has got to do to promote himself. He is down to earth."
Mayweather will step back into the ring under an 'exhibition' rule-set similar to Mike Tyson and Roy Jones Jr's meeting in November.
His opponent Logan Paul lost his only professional boxing match to KSI in 2019 in the biggest fight so far between YouTubers.
"I'm a fan of the business part - it's a great promotional fight and a way for him to earn a lot of money," Haney said.
"Competition wise? It is no competition.
"Mayweather, one of the greatest fighters to ever live, against a YouTuber who doesn't have much experience in boxing.
"It's a way for him to earn a lot of money and the world will, no matter what we say, tune in to watch."