Francis Ngannou in training to fight Anthony Joshua.

Joshua faces Ngannou on March 8.

But along with Frenchman John Mbumba, their roles became even more important last year when Ngannou put on hold his MMA career to cross over to boxing.

But Cooper admits neither him or Mbumba can take credit for the ex-UFC champion’s devastating power.

Instead, he puts it down to Ngannou’s years spent working in sand mines in Cameroon for £1.50 a day from the age of ten.

Cooper told SunSport in Saudi Arabia ahead of PFL vs Bellator: “As far as his punching power, no that was something that he naturally had.

“He dug sand mines as a kid all the way up to his early 20s.

“Of course, his DNA, his Cameroonian heritage and that hard manual labour as a kid all the way up, I feel was the main attribute to that ungodly power.”

Ngannou’s frightening power was once tested and found to be the equivalent to 96 horse power.

That means it carries the same ferocity as a 12lb sledgehammer being swung at full force or being hit by a moving Ford Escort.

And if anyone knows the pain of Ngannou’s punches, it is poor old coach Cooper.

He laughed: “I had to change my body shield three or four different times because he was killing me.

‘AJ ain’t knocking that thing out’, say shocked fans as Francis Ngannou shows off insane physique ahead of Saudi scrap.

“I was going home with injured ribs all the time but I finally got a really good body pad – and it still hurts even now.

“But I’m just barley tough enough to take it. Remember, coaching Francis Ngannou isn’t for the weak or the meek.

“The saying, ‘It felt like he got hit by a bus’, I feel that every training session, I’m used to it now.

“It’s gigantic power, it’s enormous power and that’s gonna be on display March 8th and that’s for damn sure.”

Ngannou, 37, astonishingly dropped Tyson Fury, 35, on his boxing debut but it was not enough to avoid a controversial split-decision loss.

The performance and shock knockdown was still enough to earn the MMA star another blockbuster boxing bout, this time against Joshua, 34.

It will be the second time Cooper has led the charge but his 11th bout in total with Ngannou.

And he opened up about fearing the worst whenever Ngannou’s ruthless right hand lands – but showing no remorse before it.

He said: “The Overeem fight was one that comes to memory and the Rozenstruik, absolutely. But, that’s after the knockout, after the relief of victory.

“That’s of course when the humanitarian side kicks in and you feel bad for the guys. But going into the fight, absolutely not.

“We plan on dominating, I want to make sure people understand that, if it were my way I want him to dominate and smash everyone he fights, the same way he did previous opponents in mixed martial arts.”

Ngannou pictured with boxing coach Dewey Cooper.