Eddie Hearn says Anthony Joshua was "disillusioned with the sport" when he found himself facing Andy Ruiz Jr rather than Deontay Wilder but must now "snap out of it" ahead of their rematch.

Joshua's team had long been negotiating with WBC heavyweight champion Wilder but could not agree a deal and instead made his United States debut against the unfancied Ruiz – a late replacement for Jarrell Miller.

But Ruiz stunned the boxing world by delivering a huge upset at Madison Square Garden, knocking Joshua down four times to claim the WBA, WBO and IBF belts.

A rematch is set to take place in December, but the Briton suggested in an interview with Sky Sports that he had lost "a bit of passion" for the sport ahead of the initial Ruiz fight and "wasn't boxing properly".

Promoter Hearn, who has negotiated the second fight to take place in Saudi Arabia, wants Joshua to put that behind him now and bounce back.

"I think he's just got to snap out of it," Hearn said, according to the Independent.

"I think he was disillusioned with the sport because he wanted to fight Deontay Wilder. He couldn't get that fight and, as he said in the interview, he didn't really want to fight Andy Ruiz.

"But tough, you fought him and you fought a real hungry guy.

"I think the great thing about this promotion is that now, for the first time next week, he looks a man in the eyes who is the only man to beat him as a professional.

"It's going to be absolutely huge. The whole world will stop to watch this fight."

Hearn is confident Joshua will respond to the first setback of his professional career, with a more ruthless approach potentially seeing a "nasty Josh come out".

"He ain't going to be giving Ruiz no belts to hold because he doesn't have them anymore," Hearn said.

"He doesn't even want to talk to him, he wants to knock him clean out. He didn't have that feeling last time but it's a new game now, a new game. Josh wants to take his head off.

"He's thinking, 'I've tried to be the role model, I've tried to be that guy, but people have slagged me off and said what they want to say. Now I'll say something back'.

"Now he gets criticised for calling people things - like Lennox Lewis, who has criticised him and given him sly digs his whole career.

"Josh can't win, so he's decided, 'Do you know what? Maybe it's a new approach, bring back the nasty Josh'. We hope that nasty Josh comes out for the Ruiz fight."