Barry Hearn, promoter for IBF, IBO, WBA, WBO heavyweight champion Anthony Joshua (21-0, 20 KOs) wants a deal reached sooner than later for a unification with Deontay Wilder (40-0, 39 KOs), who holds the WBC title.
The negotiations are dragging on for too long, says Hearn, and he wants things to come together soon.
Joshua is under pressure, as the WBA has already ordered him to make a mandatory defense against Alexander Povetkin of Russia.
Barry's son and Matchroom Sport CEO, Eddie Hearn, is handling the negotiations.
Wilder's handlers have sent a guarantee of $50 million for Joshua to take the contest in the United States.
However, with a mandatory order hanging over Joshua's head - time is running out to reach a deal.
"Joshua really is up for being the unified champion of the world, but inevitably the devil is in the detail," Barry Hearn told Sky Sports. "There are questions that we are in the process of answering. We've asked some and to be fair to the other side, they've come back with answers. We are still talking and we're about to answer some more detailed questions, and who knows? I never in boxing believe any deal is done until the contract is actually signed.
"We are making progress, Joshua is - as always - an integral part of the decision making process, because he's the one that does the fighting, but it's a fight he likes and it's a fight we like. We're still a long way to go in terms of detail, but that long way has to be accelerated to get an answer in the next few days or a week's time, simply because we are going to be put under pressure by the WBA: 'Are you fighting Povetkin for the mandatory?'
"We're being put under pressure because we have a couple of stadium venues saying: 'Do you really want us? Here's a contract to sign'."
Hearn explained that there are various items in their discussions which have to be agreed up - and he cautions that any of those items could potentially become a dealbreaker in the negotiations.
"We need to have a certain amount of control," said Hearn. "We need assurances on certain things, and we need contracts in place, and we need the money up front, guaranteed. But there are lots of small details, which at the last minute, each one of them could be a deal breaker. We're not going to tell you we're close, I'm saying we're on the way, but the clock is ticking and we have to move."