Anthony Joshua has labelled rival Tyson Fury a "fraud" in a furious social media tirade in the wake of a ruling that looks set to scupper their proposed heavyweight showdown in Saudi Arabia in August.

Fury has hinted he may have no choice but to face Deontay Wilder for a third time after an arbitration hearing in the US sided with the American fighter's claim that the trilogy is a contractual obligation.

Joshua accused Fury of using the move as an excuse to back out of the eagerly-awaited contest, while angry Fury responded by challenging his fellow Briton to an immediate bare-knuckle contest.

Joshua wrote on Twitter: "@Tyson_Fury the world now sees you for the fraud you are. You've let boxing down!

"You lied to the fans and led them on. Used my name for clout not a fight. Bring me any championship fighter who can handle their business correctly."

Unsurprisingly Joshua's tweet provoked an immediate response from Fury, who had taken to the social media platform to effectively confirm the Saudi bout just hours before the seemingly unexpected US ruling this week.

Amid an expletive-ridden rant, Fury wrote: "Spouting absolute s***! Your full team knew there was an arbitration going on, it was out of my hands!

"But I tell you what if I'm a fraud let's fight this weekend bare knuckles till 1 man quits? Let's put up 20 mill each!!!"

Joshua hit back as the pair traded tweets, questioning why Fury would announce they were fighting if the arbitration was in process.

"If there was an arbitration going on, why announce to the world we are fighting! The fight was signed! UNDISPUTED," Joshua added.

"Bare knuckle? You're a good kid, don't play with me Luke! I'll slap your bald head & you'll do nothing! Waste man."

Fury insists he will take out Wilder as well as Joshua.

Fury added: "Not going in to the details on line!

"You'll slap me about will you dosser please come and try Bum, i'm waiting... Femi AKA Bottlejob! 24/7 365. Ready. i'll smoke wilder first then you will get yours aswell."

Joshua's promoter Eddie Hearn has given Fury's camp a deadline of the end of this week to salvage the super-fight, but the prospects for the contest look increasingly bleak.

Some reports claim Fury is already resigned to facing Wilder again in Las Vegas in July, while Hearn is investigating an alternative contest for Joshua against leading contender Oleksandr Usyk.