Anthony Joshua should anticipate a fierce encounter in his heavyweight showdown with Daniel Dubois, cautions Johnny Fisher.

Joshua and Dubois are set to face off for the IBF world championship at Wembley Stadium on September 21, broadcast live on Sky Sports Box Office.

Fisher, the Southern Area champion and frequent sparring partner of Dubois, predicts a knockout outcome for the fight.

“I think it will be a knockout. I think Dubois is going to bring the heat and put it on Joshua. That’s what he knows, that’s his way. He’s an aggressive fighter but he’s calculating that aggression,” Fisher told Sky Sports.

He acknowledges Dubois as a formidable opponent. Dubois, a London native, is the hardest puncher Fisher has faced in the ring.

“I’ve sparred him many, many times. He’s definitely the hardest puncher, Daniel Dubois. He can seriously whack,” Fisher added.

“Dubois takes no prisoners in sparring. You’ve got to be on it. It’s a firefight when you go in with Dubois.”

Fisher also warned that while Joshua needs to be cautious, he shouldn’t be overly defensive.

“Joshua has to be careful but he doesn’t have to be too cautious and too much on the back foot because I think Dubois is open to a counter right hand himself.”

“We’ve seen how good Joshua is with the counter right hand,” Fisher continued.

“If he [Dubois] comes in, if he steps in too much, Joshua’s going to counter him with the right hand, like he did with [Francis] Ngannou.”

“I know Ngannou’s not on that level but [Joshua] has got a good straight right hand that’s lethal. Charles Martin he’s done it against. We’ve seen it many times. That’s the danger for Dubois.”

Fisher elaborated, “If I am picking a winner out of that fight, I would edge towards Joshua. A little bit more calculated. A little bit more knowhow and nous in his game and I think that could tip it in his favour. But if Dubois lands on his chin, that could bring back all those memories [of the Andy Ruiz defeat] for Joshua.”

This Saturday, Fisher is preparing for his own fierce battle against Alen Babic at the Copper Box Arena in London, saying: “I’d expect him to be right there in front of me, and that’s not a good place to stand.”

A strong performance, Fisher believes, could position him for a British title fight against Fabio Wardley or Frazer Clarke.

“You win the next fight and the picture becomes a bit clearer,” Fisher said. “I think people are starting to see that there’s potential there to go beyond just being a ticket seller. I’m a prospect and I’ve got the potential to maybe win an English, British title, maybe European title and who knows I might even fight for a world title. That’s what you want to get to. That’s the aim.”

Clarke and Wardley fought to a draw in an epic British heavyweight title fight in March, and negotiations for a rematch are ongoing.

“Fabio Wardley I’ve sparred loads, Frazer I’ve sparred before and I just have admiration for both of them guys. They really did the belt justice that night,” Fisher said.