Andy Ruiz Junior watches as the referee counts after he knocked-down Anthony Joshua. Photo: Frank Franklin II/AP

When Anthony Joshua was finally cleared of lasting damage by a brain scan in the dressing room, he emerged to discount retirement at 29, and insisted he will invoke his rematch contract clause with shock world heavyweight title conqueror Andy Ruiz Junior.

The return bout for the WBA, IBF, WBO and IBO belts he lost to a devastating seventh round KO in Madison Square Garden is most likely to take place under the roof of Cardiff’s Principality Stadium in November.

But there is a chance that if this five-knockdown thriller promises big TV money in the US, it could be transferred to Las Vegas.

Joshua said: “I will come back from this defeat stronger and continue my learning curve.”

Joshua suggested that he will be the one to KO Ruiz when they clash again, having knocked him down first in the opening round here.

But his promoter Eddie Hearn warned that the rematch is a “must win” because Joshua’s options will be “nothing after that”.

Joshua said: “Winning is everything. I am not going to sit here and say ‘Losing is fine’. Not in my book.

 But if you do happen to lose, adjust and bounce back. But I do not condone losing in any form. This is war, battle, so what’s next?’

Joshua, who lost the IBF, WBA and WBO world titles, was asked about potential fights with WBC world champion Deontay Wilder and Tyson Fury.

“I still want to compete with those men, but a rematch with Andy Ruiz Junior is where we are at,” he said.

“I’m still a champ, and I will rectify it to get the belts back.”

Hearn said Joshua got sloppy, and expects the defeat to devastate his fighter, adding Ruiz had pulled off one of those big upsets in heavyweight history.

“I don’t think he really knows a lot about the fight after the third round,” said Hearn.

“Despite the fact that he kept getting up, I think he was concussed, I think he never recovered.

“If he was composed and a little bit more experienced, I think he’d have taken him out in the third round, but he paid a terrible price.

“But he should be beating Andy Ruiz.’

Daily Mail