Motivated Mike Tyson loses 45kg for comeback fight against Roy Jones Jr

Mike Tyson claims he has lost 45kg for this weekend's comeback fight with Roy Jones Jr and has proudly been showing off his body.

The 54-year-old former heavyweight boxing champion stripped off his shirt on the national TV show Good Morning America to prove his point on Tuesday.

"This is where it’s at, man! This is where it's at. This is where it’s at, brother!" Tyson told host TJ Holmes, as he revealed his chest.

Tyson takes on Jones in an exhibition fight in California on Sunday (NZT) and said he didn't lack motivation to get back into fighting shape with plenty of encouragement from home.

"I became a vegan. My wife told me to get on a treadmill. I went from 15 minutes on the treadmill and ended at two hours," he said, saying he felt like he had gone back in time.

"I had to lose 100 pounds. But other than that I've always done this my whole career," he said.

How the fight pans out is fascinating, and former heavyweight champion David Haye has thrown out a theory that Tyson's bursts of activity will be short, and he'll need to make them count against the clever Jones, 51.

"Mike Tyson, I think can roll back the clock for 5-10 seconds, twice a round maybe," Haye told Seconds Out.

"I don’t believe he is going to have many bursts. The first burst and how much rest he needs after is this. I have seen some fantastic pad and bag work from Mike Tyson. But I have only seen it in 2-3 seconds bursts.

"I want to see what happens when Mike Tyson lets his hand go for 10 seconds ... pins Jones, gets the ropes.

"Roy Jones has got a very, very good defense, good eyes. He can see what’s coming, and he should be able to see Mike Tyson’s shots coming because he is a lot older and slower."

Tyson hasn’t fought since 2005, when he quit on his stool against lowly ranked Kevin McBride.

Jones, a multi divisional world champion, last fought in February 2018.