Promoter Eddie Hearn expects Amir Khan to make a final decision regarding his next return within a week's time.
Khan is mulling two deals that are currently on the table.
He has the long-awaited showdown with domestic rival Kell Brook in the headline bout of a Sky Sport Box Office card, which is being targeted for the first quarter of 2019. And there is also a $5 million guarantee to face WBO welterweight champion Terence Crawford on March 23, as part of an ESPN Pay-Per-View from Madison Square Garden in New York.
The contest with Brook is worth more than double of the offer to face Crawford, according to Hearn.
Brook returned to the ring on Saturday night in Sheffield, and looked very ordinary in winning a twelve round decision over huge underdog Michael Zerafa.
But the logic for Khan, says Hearn, is the scenario of facing Crawford - and still being able to face Brook in the aftermath.
A loss to Crawford, regarded by many as the best pound-for-pound fighter in the sport, would leave Khan with some options - like Brook. But a loss to Brook would be devastating for Khan's career.
"I've told Amir it is now or never - I think he will decide in the next week. He may sign the Crawford fight. Before tonight I would have said he would go with the Crawford fight... (but) Kell looked average tonight. If you weren't sure before tonight, which he's not because it is one or the other, then surely that is going to make you more sure," Hearn told Daily Mail.
"I'm not saying Amir thinks he is going to lose to Crawford but there is definitely the element of, "If I lose to Crawford I can come back and fight Brook. But if he loses to Brook it is, 'Oh my God' and Brook feels the same. They're both petrified of losing. It will kill them forever. All their world titles, unifications - it will be like George Groves. He is remembered for getting knocked out by (Carl) Froch, I know he went on and did brilliantly but he's still remembered for that moment and that is what losing this fight would be like for these guys.'
"Are they still in the primes of their career? There is an argument that Kell is not as good as when he fought Shawn Porter (to win the world title in 2014), maybe Amir is not as good as when he boxed (Marcos) Maidana (in 2010) but they're still world class fighters. After that performance, I have to say Amir is the favourite. It sells out any arena in double-quick time. I think it sells around 60 or 70,000 (tickets). People will forget about that (Zerafa) performance two days later. It is chip paper. People will know about the history and the build-up. When they get together it will be epic."