World heavyweight champion Anthony Joshua has one "defective gene" in his game, according to BBC Radio 5 Live boxing expert Steve Bunce.
The 28-year-old Londoner has won all of his 19 bouts since going professional in 2013, knocking out all 19 of his opponents.
Joshua will defend his WBA and IBF world titles against 36-year-old Frenchman Carlos Takam in Cardiff on Saturday night.
Takam is a mandatory challenger and is considered a massive underdog after stepping in as a last-minute replacement for the injured Bulgarian boxer Kubrat Pulev.
It will be Joshua's first appearance in the ring since his titanic heavyweight title fight victory over Wladimir Klitschko at Wembley Stadium in April.
The Watford born boxer wanted a re-match with Klitschko but the 41-year-old Ukrainian announced his retirement on 3 August 2017.
Fans loved the thrilling bout between two of the finest boxers of their generation but Bunce believes fighting like a "lunatic" is not a positive aspect of Joshua's game.
"He loves those long, drawn out, sucker punch, lunatic heavyweights from the 70s," said Bunce on BBC 5 Live, as per Business Insider. "And Joshua's got a bit of that in him.
"That's his one defective gene, he might like slugging too much."
Bunce did admit that Joshua's 'defective gene' - which is yet to cost him a fight - is the reason why he's so popular amongst boxing fans.
"It's not because Joshua is in the 'never put a foot wrong' business, it's because people like him and know they're going to get a fight.
"They're going to be entertained for their money."
Bunce said Joshua's preferred fighting style opposes the basics taught by his head coach Rob McCracken — he even admitted this in an interview, according to Bunce, where he said: "Don't tell Rob, but I actually like those fights."
British fans absolutely love the 2012 Olympics gold medallist and a win against Takam will all but wrap up the Sports Personality of the Year award.
He'll become the first Boxer to win the award since Joe Calzaghe in 2007.