Deontay Wilder has warned Joseph Parker he must knockout Anthony Joshua if the New Zealander has any ambition of winning their heavyweight unification fight.

Joshua and Parker meet in Cardiff on 31 March when the WBA, IBF and WBO belts will all be on the line, the first time ever two reigning champions from boxing's blue-ribboned division have met in the United Kingdom.

WBC champion Wilder is targeting a fight with the victor should he see off Luis Ortiz on 4 March but he is openly advising Parker who he would presumably prefer to face later this year.

The 32-year-old has regularly insulted the Olympic gold medallist; criticising everything from his physique to his stamina which he believes was exposed in his victory over Wladimir Klitschko.

And Wilder's latest comments regarding Joshua - who has a 100% win and KO record from his 20 professional bouts - have seen him tell upcoming opponent Parker to go for the kill.

"I've always said 'later rounds'. I see that fight going later rounds if Joseph Parker is smart in what he does," said Wilder, in quotes carried by Boxing Scene.

"He has nice movement and is able to execute on all of the opportunities that he sees with Joshua. Because Joshua can't move his head.

"He's a muscle, body-building type of guy. You've seen my dance? [chuckles] With that, if he's able to calculate what he needs to do in the ring - because the ring has a lot of secrets - if he's able to do things he needs to do, I see late rounds.

"But, like I said before, I think they're going to have to knock Joshua out because they're not going to give it to him."