Anthony Joshua

Ruiz shocked the world by unseating the British heavyweight in June, with Joshua delivering an underwhelming performance at Madison Square Garden.

The WBA, IBF and WBO and belts will again be on the line for the December 7 rematch, which is controversially being held in Saudi Arabia, and Ruiz will not give them up easily.

Joshua lost his WBA, WBO and IBF belts to Ruiz in a stunning upset at Madison Square Garden in June.

Matchroom Boxing last week confirmed a rematch for December 7 in Riyadh, with Ruiz having refused to fight in Britain.

The Mexican-American is yet to comment on the scheduled fight, but Matchroom promoter Hearn told a news conference on Monday: "Both fighters signed for this fight. The governing bodies have been informed."

Ruiz caused a major upset when he defeated Joshua - making his debut in the United States - by technical knockout in the seventh round of the June 1 fight to claim the WBA, IBF and WBO titles.

A rematch is likely to take place in November or December, though a venue is yet to be decided.

Joshua's choice is Cardiff's Principality Stadium, but Ruiz has refused to fight in the UK and a neutral venue is expected to be confirmed.

However, Joshua insists he is paying little attention to the negotiations and is solely focused on regaining his titles.

Ruiz was sensationally crowned IBF, WBA and WBO world heavyweight champion by stopping Joshua at Madison Square Garden at the start of this month.

The Mexican is set to face Joshua in a rematch later this year and says the 2012 Olympic champion does not have the skills to reclaim his belts.

Ruiz said: "The rematch is going to be the same. I am going to be more prepared and more ready.

"I know his flaws. I can do a lot better. The only thing that he can do is just run around, he's not good at boxing."

Hearn said a deal has been clinched that will see the rematch take place in November or December.

Joshua lost his WBA, IBF and WBO heavyweight belts after a shock seventh-round TKO at the hands of challenger Ruiz at Madison Square Garden in New York on Saturday.

The new fight deal was struck in accordance with what Joshua and trainer Rob McCracken wanted, Hearn indicated.

After visiting the canvas four times inside seven rounds, a dream American debut at Madison Square Garden unravelling into an unforeseeable nightmare, the former IBF, WBA and WBO world heavyweight champion emerged for a delayed post-fight news conference with a smile and good manners.

"I've dealt with some real big losses in life and bounced back. I feel like this is just part of a journey that I'm on," he said, having warmly embraced Ruiz in the ring afterwards.

Anthony Joshua, a chiseled, towering, undefeated British world heavyweight champion with a wide grin and an easy disposition, came to Madison Square Garden on Saturday night to make his United States debut. He had talked before the fight about not just winning, but winning in style, and about the potential for a megafight down the road against Deontay Wilder, an undefeated world champion from the United States.

WBA, IBF and WBO champion Joshua was originally set to face Jarrell Miller in a heavyweight showdown in New York City on June 1, but that bout was scrapped after Miller failed drugs tests.

Ruiz stepped up to take Miller's place, with the American-born 29-year-old – who is of Mexican heritage – having won 32 of his 33 professional fights.

On Wednesday, Joshua urged current WBC champion Wilder to clear the path for an undisputed heavyweight title fight, should the Briton beat Ruiz.

Joshua makes his seventh world title defence and United States debut when he takes on Andy Ruiz Jr at Madison Square Garden in New York on Saturday.

And coach Rob McCracken wants the IBF, WBA and WBO champion to make a blockbuster showdown with Wilder his next priority amid calls from promoter Eddie Hearn for "excuses" to be set aside.

The American gave a stunning exhibition of his power earlier this month, taking just 137 seconds to knock out Dominic Breazeale and defend his WBC heavyweight title.

"It will happen," McCracken told Sky Sports.

Wilder needed just 137 seconds to knock out Dominic Breazeale and retain his WBC heavyweight title on Saturday, improving his record to 41-0-1.

The American drew with Tyson Fury in December and there were calls for a rematch with the Brit or bout against WBA, IBF and WBO heavyweight champion Joshua.

Wilder – whose knockout of Breazeale was the 40th of his career – said a fight with Joshua would happen, but he remains unsure when.