Unbeaten British heavyweight Johnny Fisher insists Daniel Dubois is the biggest puncher he has ever been in the ring with and believes he is capable of shocking Anthony Joshua at Wembley.

Joshua and Dubois are set to face each other at England's national stadium on September 21 with the IBF heavyweight title on the line.

Two-time champion Joshua is the strong favourite to regain his crown after winning his last four fights, including a spectacular two-round demolition of Francis Ngannou in March.

But Dubois has also proved he belongs on the world stage by winning two on the bounce in Saudi Arabia, and he came through some tough moments to see off the previously undefeated Filip Hrgovic last month.

Having been upgraded to IBF champion after Oleksandr Usyk opted to vacate the belt, Dubois will make his first defence against Joshua in a domestic dust-up.

And Fisher - who has sparred several elite heavyweights such as Tyson Fury - is adamant it will be no walkover for Joshua, after revealing exactly how hard Dubois hits.

'I've sparred Dubois, I've sparred Fabio Wardley, Tyson Fury, Derek Chisora, Carlos Takam, Filip Hrgovic and many more but Dubois is the biggest puncher I've ever faced by far, Fisher told Mail Sport. 'He can seriously, seriously whack.

'He's got more than a puncher's chance. He's got a good jab himself and the way he fought Filip Hrgovic, came through the first couple of rounds getting punched and getting hit quite regularly showed he's got a good chin and he can come forward so it's not a walkover by any means for Anthony Joshua.

'If he rattles Joshua early he can send a few warning signals and he can get it done.'

Fisher cannot wait for the British pair to settle their differences in front of up to 100,000 fans at Wembley, but despite backing Dubois to cause Joshua problems, he admitted there are factors in AJ's favour that could give him the edge.

'It's a great fight and it's brilliant that it's happening in England in Wembley,' Fisher added.

'If I'm thinking of it logically I think Joshua's got a little bit too much know-how, a bit too much experience and should be the favourite in that fight.'

The heavyweight division is thriving at the moment, with another huge showdown on the horizon between Fury and Usyk.

Usyk beat Fury via split decision in May to become undisputed champion, but the Gypsy King will get his shot at redemption on December 21 when they square off again in Saudi Arabia.

Reflecting on why Fury fell short the first time around, his ex-sparring partner Fisher felt Fury's weight and in-ring antics cost him in the gruelling 12-round contest, but backed him to put things right in the rematch.

'I thought it was a very close fight. I thought or two rounds to Usyk is probably fair, but it wasn't as if Fury was out of the fight,' Fisher said.

'I thought round six or round seven if he turned the screw a little bit more he could have got rid of Usyk, but Usyk just stepped it up and found another gear of work rate and that helped him nick the fight. 

'In terms of what he could do differently, I don't think he needed to lose all that weight. I don't think losing weight is always a good thing. I think being the bigger, stronger man, you should use that to your advantage. 

'And maybe a little less showboating, he could have had a little more energy for those last couple of rounds. I really do think Tyson can do it and I hope he does, as a Brit. He's been great for British boxing and I'm excited to see him do the job.'

The role of Fury's dad, John, around the Usyk fight has also been questioned by some fans and pundits after he was seen headbutting a member of the Ukrainian's team in the build-up.

He then joined Sugarhill Steward and Andy Lee in his son's corner on fight night, leading to accusations of Fury becoming confused with who to listen to for instructions.

Fisher - whose own father has become a social media sensation for his famous 'bosh' clips - conceded John did 'overstep the mark' with the headbutt, and called for Fury to change things up in his corner if he wants to exact revenge on Usyk. 

'Whenever I've been around John Fury, he watched our sparring once a few years back when he was fighting Deontay Wilder for the third time, what a good man, really respectful,' said Fisher.

'I think he does play up for the cameras, especially since being involved in that Misfits world. I remember him smashing the glass and just making a nuisance of himself, but maybe he overstepped the mark a bit in the Usyk fight. It probably didn't need to be sold or need any sort of input from him at all because it's the undisputed championship of the world. It sells itself. 

'I wasn't impressed by the headbutt like most people but I also believe people can make mistakes and then they can be forgiven for them. I think he's got a great relationship with Tyson. My dad knows to stay out the way. He knows boxing but he's not a boxing trainer, he's not a professional boxing man so leave that to the professionals I'd say. 

'I definitely wouldn't want my dad in the corner because he'd be a nervous wreck. I just think you need one voice in the corner and that's your head trainer. That's all that's needed.'

Fisher has his own fight on Saturday night when he takes on former world title challenger Alen Babic at the Copper Box Arena.

It will be Fisher's first time topping the bill, and the popular Essex boxer revealed he has sold 3,500 tickets to fans from his dad's living room.

Babic appears to be a significant step up on paper, but Fisher has won 10 of his 11 fights inside the distance, and is expecting to get another stoppage win in the capital. 

Fisher stated: 'I am always trying to be a fan-friendly fighter and Babic is one of them as well. He brings all-action, brings the heat to his opponents.

'I'm ready for 10 really gruelling, hard rounds. I've prepared better than I ever have, but hopefully I can show that I can come through this and show what my level is.

'Babic is going to come out swinging, he's going to try and wear me down bit by bit over the rounds thinking that he can get me later. But I'm too strong, too fast, too powerful, I've trained too hard. 

'I've got too much boxing skill which I haven't had to show too much of yet. I think I'll show that bit of skill and the power will be too much for him and I'll get him out of there.'

Saudi Arabia has hosted the majority of boxing's biggest events in recent months, particularly in the heavyweight division, and Fisher could soon get the invitation to head over to the Middle East.

But 'The Romford Bull' insisted he is one of the few fighters in no rush to join the likes of Joshua, Fury and Usyk in Saudi Arabia, and is focused on continuing to build his fanbase closer to home instead.

'I think the Romford Army would have a lot more fun in England, in Vegas, in these sort of places,' he said.

'I'd love to stay here but we're all professional boxers, we've all got to earn our money, we've all got to make a living. It's very hard for a professional sportsman in boxing to earn money so if you get an opportunity over there and it's a big fight you can't say no. 

'But for me now, I'm very grateful for the living I can earn here in England, places in Europe and I'd love to fight in Australia at one point because we've got a big fanbase over there. Saudi Arabia isn't the pull for me right now, but who knows in the future.'