Amir Khan and Kell Brook would "kick themselves forever" if they fail to agree a fight, believes promoter Eddie Hearn.
Rivals Khan and Brook both have their next bouts scheduled, against Samuel Vargas and Brandon Cook respectively, as a possible collision course continues.
"After [their next fights], we'll be looking to get that fight signed. It's the biggest fight out there, but both have options," Hearn told Sky Sports.
"Brook has the Charlos, and Jarrett Hurd. Tough fights at 154lbs.
"He can drop back to welter for Khan, who also has options - Manny Pacquiao, Danny Garcia, Errol Spence Jr.
"But they will kick themselves forever unless they get it over the line.
"Fingers crossed - December, if they can both keep winning, we'll get there for Khan vs Brook."
Since Brook was beaten by Spence Jr and Khan suffered a knockout loss to Saul 'Canelo' Alvarez, the British pair have rebounded with victories.
Brook needed less than two rounds to stop Sergey Rabchenko, before Khan beat Phil Lo Greco inside 40 seconds.
Brook is next due to face Cook on the July 28 undercard to Dillian Whyte vs Joseph Parker, live on Sky Sports Box Office, while Khan will face Vargas on September 8, live on Sky Sports.
Khan said this week about Brook: "I'm the one who made this fight closer, I made a deal with Eddie (Hearn) and Matchroom, hopefully, to get this one done.
"When he first started calling me out, no one really paid attention, I let him bark and talk, now he's getting out of his boots and needs to be put in his place.
"But it has to be at 147lbs, if that fight is going to happen then it happens at 147lbs."