WBO, IBO, WBA, IBF heavyweight champion Anthony Joshua (21-0, 20 KOs) has issued a warning to Deontay Wilder (40-0, 39 KOs), who holds the WBC heavyweight crown.

The two camps are currently in serious negotiations for a highly anticipated unification in the coming months.

Joshua is now the owner of four world titles - after picking up the WBO title with a twelve round unanimous decision win over Joseph Parker in March at Principality Stadium in Cardiff, Wales.

A few weeks ago, Wilder's handlers sent Joshua an guaranteed offer of $50 million to stage the fight in the United States.

The two sides are still going back and forth on the details.

“Luckily, we’ve got enough time to make the fight happen and we’re working on it. We’ve just sent another draft email over to them. It’s just the technical jargon that we’re going through right now," Joshua told The Sun.

Back in March, Wilder recovered from a dire seventh round to score a tenth round knockout of undefeated Cuban puncher Luis Ortiz at the Barclays Center in Brooklyn, New York.

Wilder has cautioned that he might close the book on Joshua in the early moments of their potential showdown.

Joshua, a 2012 Olympic gold medal winner, says there is no fear of Wilder's power - and the British superstar plans to be very aggressive in the early rounds.

“I ain’t got nothing to lose and I’m [going to] rain down hell on him – I’m going to f*** him up bad. You’ve seen it, I can go to hell and back. I enjoy it there as well, this time I’m going to own it," Joshua said.

“We’re big hitters, so for sure I’m going to be throwing a lot of combination punches and it’ll be interesting. I think he’ll be trying to pick punches. I’ll just be coming forward and swinging a lot of combinations, just trying to catch him and hurt him early on.”