Tyson Fury's father, John, has revealed the 35-year-old was suffering with a lung problem prior to his recent victory over Francis Ngannou.
The Gypsy King was the strong favourite for the fight in Saudi Arabia and won via split decision, despite being knocked down in round three.
Fury did, however, look a shadow of the man who has overcome the likes of Deontay Wilder and Wladimir Klitschko during the course of his career.
Now, the boxing star's father John has shed light on issues prior to that bout.
Tyson Fury was suffering with a lung problem and had a 'funny colour face' before his recent victory over Francis Ngannou
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Speaking to GiveMeSport, he revealed his son had an issue with his lungs in the days leading up to the fight.
And he also revealed Fury's face turned a 'funny colour', too.
"Ngannou probably fought the worst version of Tyson I have ever seen, physically and mentally," he said.
"Even in the dressing room, his face was a funny colour.
"I was watching him spar the week before, and I wasn't impressed.
"His lungs were all over the place during the week, I was taking notes of how hard he was breathing after rounds.
"It could be where we were at, but things weren't improving.
"He had a terrible week, one of his worst ever, but he still did enough to win.
"If Tyson wasn't able to go back to the old version of him in the later rounds he was f***ed.
"But he hadn't been training to do that, and he was instead trying to throw bombs.
"I saw it coming, and I knew this would happen.
"What was he doing trying to blow him away? He wasn't giving it his full wit, his full concentration, and he thought it was going to be easy because people were telling him that."
Fury is now gearing up for his fight with Oleksandr Usyk.
The duo had been due to face off on December 23, with the Gypsy King even threatening legal action in the event of a postponement.
Yet the two men will go to war in February instead, having confirmed a new date for their fight last week.
Many are writing off Fury given the way he underwhelmed during his recent victory over Ngannou.
Ricky Hatton, however, has told talkSPORT he's convinced the 35-year-old will bounce back and silence his critics.
“I think Tyson will certainly be a lot better than he was last time," he explained.
“And he’ll certainly have to be, he doesn’t need me to tell him that, but I think he will be.
“The last fight, I think he simply just took the fella – even though he was a monster of a man – I think he took him little bit lightly.
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Tyson Fury and Oleksandr Usyk are due to meet in the boxing ring on February 17
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“I think he could’ve come in in a little bit better shape than what he did do.
“I went to Saudi Arabia for the fight and it was such an occasion – I think Tyson forgot what he was there for!
“He forgot what he was there to do! It was such an occasion and he was fighting this UFC fighter who’s not had a boxing match before in his life and I think he just took it all a little bit lightly.”