Tyson Fury's promotor, Frank Warren, has dismissed fears from the heavyweight boxer's outspoken father about the level of training he's seen from his son.
A heavyweight unification fight between Fury and Usyk was confirmed last month to take place on February 17 in Saudi Arabia.
One of them will be crowned the first undisputed heavyweight champion since Lennox Lewis in 1999.
Usyk was in the crowd to watch Fury's last fight against MMA star Francis Ngannou when the 'Gypsy King' was knocked down to the canvas.
John Fury is concerned for his son
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Both fighters are now in their respective training camps to prepare for the blockbuster event in just two months and Fury's dad has not been impressed by what he's seen.
"His training's in decline and his camp's in a bigger decline," he said.
"It's not a camp, it's a circus."
Fury Sr continued: "Unless you're gonna get the eye of the tiger back and go back to the old ways and get the hunger back - sweat, blood, s*** and tears.
"Because Usyk's doing that - sweat, blood, s*** and tears.
"And he's got disciplined, professional, great people around him, and I don't think Tyson has that. I really don't.
"But those concerns aren't shared by Warren, who has faith in Fury picking the right team around him to best prepare for the unification bout.
"Tyson's the guy getting in the ring," Warren told Boxing Social.
"His dad has obviously got his views. Everybody's got a view.
"Obviously his dad cares about him but, at the end of the day, Tyson's getting in the ring and it's his decision who he has to train him."
Fury and Usyk had been locked in negotiations for several months prior to last month's announcement, with fears the fight would never happen.
John Fury wants his son to change his training camp
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But after the unification bout was confirmed, both fighters took to the stage in a fiery press conference with Fury launching into an explosive rant aimed at his opponent.
He said: "I already relieved one Ukrainian [Wladimir Klitschko] of all the belts and I'm going to relieve that idiot of the belts that I gave him! Including my Ring magazine that I vacated last year so I could win it back three times, sausage!
"I'm going to bust him, sausage, ugly little man, rabbit. 'Run rabbit, run rabbit, run, run, run!' I don't want a 'more more' [in response to Usyk's gesture], you know what's coming, you're getting smashed to pieces sausage.
"You're fighting the best British heavyweight there's ever been, the f****** dauntless in these waters, me.
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"You beat all the rest of them, but you ain't beat Tyson Fury yet sausage. Look at him, his heart's pounding now, he's like a little p****y with an earring in, s*******!
"His b******* have shrivelled up now they have, little sausage, a sissy with an earring in, you f****** p***y! Getting knocked spark out!"
