London - Anthony Joshua has urged Deontay Wilder to be "realistic" about who is the bigger draw card should the heavyweight champions meet in a blockbuster unification fight. 

Should such a bout between British boxer Joshua, the International Boxing Federation and World Boxing Association title-holder and American rival Wilder, the World Boxing Council champion, take place it could be one of the richest in history. 

But no serious talks have yet to take place between the two camps, with Joshua first having to overcome the World Boxing Organisation champion, Joseph Parker, whom he takes on in Cardiff a week on Saturday. 

However, 2012 Olympic champion Joshua said the brash Wilder needs to accept the Briton has greater spectator appeal in the United Kingdom than the American does in the States, and so should be the one to cross the Atlantic for any unification bout. 

"If he was serious about the fight, we'd do serious negotiation," Joshua said on Wednesday. "If not, (he should) stop hooting and hollering because we'll just freeze him out. 

"We're in a position where I've still got great top-10 challengers I can compete with. He's in a position where the broadcasters ain't interested in (him fighting) Joe Bloggs anymore." 

Joshua added: "I know where I am going with my career. If he wants to be a part of this and jump on the train and come to the UK, he has to be realistic and stop living the fantasy. That is all we are saying, be realistic in negotiations. 

"What we've got to offer is going to be 10 times more in terms of financials - because that's what it comes down to -- than he's looking at in America. 

"If he offered me 10 times more money to fight than what I am looking at in the UK, I would go there to fight him. But he is coming here. We are doing the offering, he hasn't offered us. Take it or leave it." 

The trash-talking Wilder is set to be among a crowd of 78 000 at Cardiff's Principality Stadium for Joshua's bout against New Zealander Parker. 

"I'd love to sit down and talk with him," said Joshua's promoter Eddie Hearn of a possible meeting with Wilder. 

"There's a lot of bluster with Deontay but he's not an idiot," said Hearn. 

"He knows what he's doing and he's doing a good job in attracting people to fights, but I think this fight will be made a lot quicker than people think. I believe it will be in 2018."