Kell Brook's father has revealed he is nervous for the first time about his son's chances as he prepares to fight the dangerous Gennady Golovkin.
On Saturday at London's O2 Arena, Brook will step up two weight divisions to challenge Golovkin for the IBF, IBO and WBC middleweight titles.
Golovkin's power, which has inspired 32 stoppages within his 35 professional victories, means he is considered the world's most destructive puncher. He has been described by several observers as 'the new Mike Tyson'.
There remain rumours that he overpowered the world's leading light-heavyweight Sergey Kovalev in a sparring session, and he is widely avoided by other contenders.
Brook's father Terry Thompson has overseen his son's upbringing in Sheffield, and experienced him being stabbed during a night out in 2007 before surviving a life-threatening machete attack while on holiday in Tenerife in 2014.
Brook also won his IBF welterweight title by out-boxing America's powerful Shawn Porter in 2014, so Saturday is not the first time Thompson has had reason to fear for his son's health in or out of the ring.
However, asked how he felt when the fight was made, he told Press Association Sport: "What goes through your mind is Kell's health. You know he's in a serious fight, but that's what Kell's always been. You're naturally going to worry.
"I believe in Kell. Sometimes I think it's a lot more dangerous out there on the streets.
"I do know in England we've got the best people ringside, and from previous experience that they're in good hands, so you put that to one side.
"You're talking about two of the world's best pound-for-pound fighters, they can both punch. It's a severe sport.
"As a parent, this isn't one of them fights where you think, 'It's a walk in the park'."
As for nerves, Brook's father added: "I've never really had any, because I know Kell, but if you ask me for this particular fight, yeah, I did have that thought, 'Hold on, they're both serious warriors, serious punchers'."
Brook remains the significant underdog against Kazakhstan's Golovkin, but little over a year ago the South Yorkshire fighter stopped Frankie Gavin in such a one-sided beating that Gavin vowed to drop down in weight.
The Englishman has also experienced the difficulty of coming through a close fight, as when he was bleeding heavily after having his nose broken by Carson Jones in 2012.
Thompson added: "Like with Golovkin, all the fighters have got a mum, a dad, who feels that pain.
"We're all aware that when you go into this, that's what can happen. I always think, on a Saturday night, there's a lot of lads who go out onto the town, and lots all over England get knocked out on a Saturday night for absolutely nothing.
"Provided they're hydrated well, looking after themselves and not killing themselves to make weight, in 99 percent (of cases) there's no real harm done."
Thompson has from time to time felt sympathy for an opponent of his son.
"I've thought it with Kell as well; anxiety when I saw him in the Carson Jones fight, I didn't enjoy that one," Thompson added. "But this is the game they're in."