A unification bout with WBC champion Wilder has been touted for WBA, IBF and WBO titleholder Joshua, who claimed the latter belt with a unanimous decision over Joseph Parker last month.
A clash between the two unbeaten boxers is the fight everyone wants to see and on Wednesday, American Wilder announced he had something in the mail for Joshua – a $50m offer.
"I got something special for you," Wilder tweeted. "And by the way, all the money's in the bag."
Wilder's promoter Shelly Finkel gave Joshua and his camp until the end of the day on Thursday to accept the offer.
"We want [Joshua] to fight Deontay in his next fight and we offered him $50m," Finkel told Sky Sports. "If he accepts it, it will be there. Al Haymon and I have never not delivered what we've offered.
"We were offered $12.5m [£8.8m] to fight him but we have offered four times that. If [Joshua] says he is not going to take $50m, it means he doesn't really want to fight him next.
"It was $50m against 50 per cent. He said, 'get me $50m against 50 per cent and I'll take it the next day, I swear'."
However, Joshua's promoter Eddie Hearn said he has a meeting set up with Finkel for Friday, while he remains doubtful the money is for real.
"With all due respect to Deontay Wilder, I don't believe he has $50million," Hearn told Sky Sports.
"However, if they actually send some formal paperwork and a contract along with further details on how this money will be secured, we will definitely have to take this seriously."
Photo Getty Images. Caption: WBC heavyweight champion Deontay Wilder