American fighter Deontay Wilder has reportedly been offered a $12.5 million contract to fight unified heavyweight boxing champion Anthony Joshua.

As the showdown is expected to generate upwards of $80 million, Wilder's representatives claim the deal is currently "an insult."

Wilder called Joshua "a joke" and insulted the Briton even further on his official Instagram account.

America's big-hitting heavyweight is set to reject a $12.5 million contract to fight unified world boxing champion Anthony Joshua after calling him "a joke."

Alabama big man Deontay Wilder is a 6-foot-7 athlete who has knocked out 39 of his 40 opponents in a professional boxing ring to date.

WBC heavyweight champion Wilder is on a collision course with Joshua, who holds the WBA, WBO, and IBF titles. If they fight, the winner will hold all four of the major heavyweight belts and become the undisputed champion in boxing's most prestigious weight class.

But, before they even agree to a fight, they have traded verbal blows while the promoters involved argue over money.

"If [the contract offer] is anything within reason, we'll do it," Wilder's representative Shelly Finkel said to global boxing publication The Ring earlier this week.

Wilder, so desperate to take on Joshua, once said he'd give up two key advantages to make the bout happen — he'd fight in Britain, Joshua's home country, and he'd even let Joshua have the bulk of the profits.

But then came an offer in the form of a $12.5 million "take it or leave it" bid — and Wilder's team said it was too meagre for a fight of this magnitude.

This is because this bout could generate $80 million to $100 million, according to The Ring panelist Adam Abramowitz.

He tweeted: "Sources told me that [Joshua's promoter] Eddie Hearn offered Wilder's side a $12.5 million take it-or leave it offer. For a fight with potential revenues of $80 million to $100 million, that offer is far below 20% of potential revenues."

When Finkel received the offer he was reportedly unhappy, and would only tell The Ring that they were "preparing a response."

New York boxing promoter Lou Di Bella, who also represents Wilder, said the $12.5 million deal was insulting. "If you’re going to make an offer that insults Deontay Wilder, it’s obvious Eddie doesn’t want the fight right now," he said.

Joshua is "a joke"

Anthony Joshua. Getty Images

Wilder made a guest appearance on Viceland's YouTube show Desus & Mero on Tuesday and used the platform to accuse Joshua and Hearn of cowardice.

"They scared of me," Wilder said. "I've said it before, he should take that 'f--- fear' patch off his trunks because that don't apply to him when it comes to me. Anthony Joshua, he a joke."

One day later, Wilder reiterated his point on his official Instagram channel.

He said: "It’s obvious at this point they don’t want no smoke… at some point in life a boy must detach his lips from mum nipples and become a man, I’m just saying."

It’s obvious at this point 40-0 w/39ko’s they don’t want no smoke... at some point in life a boy must detach his lips from mum nipples and become a man, I’m just saying🤷🏿‍♂️... 📸: @thisisamandaw #BombZquad #ScaredSenseless #Wow😂😂😂 A post shared by Deontay Wilder (@bronzebomber) on Apr 10, 2018 at 10:47am PDT Apr 10, 2018 at 10:47am PDT

It did not take long for Joshua to respond, as the Briton accused Wilder and his team of lacking professionalism because of the way they have handled contractual negotiations so far.

"We offered them a lucrative deal and we are just waiting to hear if he's serious or not," Joshua said on Sky Sports.

"They like to jump on social media, rather than emailing us back in a professional manner. I don't understand where they're coming from, nevertheless, there's many heavyweights out there that are serious."

If negotiations for this fight have contained this many verbal jabs, you can assume an actual bout — if one can even be agreed — will pack a knockout punch.