Billy Joe Saunders is close to finalising a deal to face boxing's best-paid fighter Saul 'Canelo' Alvarez in Las Vegas on 2 May.
The Briton, 30, will put his WBO world super-middleweight title on the line against Alvarez.
Alvarez has one loss - to Floyd Mayweather in 2013 - in a 56-fight career.
The Mexican will again fill the Las Vegas date to align with his country's Cinco de Mayo weekend celebrations.
WBA super-middleweight champion Callum Smith was in line for a shot at Alvarez but Saunders will instead secure his toughest bout to date.
Reports in the US claim Saunders will earn the biggest purse of his career against a man who agreed a deal worth an estimated £278m with streaming service DAZN in 2018.
Saunders is undefeated in 29 bouts and previously held a world title in the 160lb middleweight division before moving up to do the same in the 168lb super-middleweight division.
He defended his title in a laboured knockout win over Marcelo Esteban Coceres in Los Angeles in November.
Alvarez has held full world titles in three weight divisions and also held a minor version of a world belt at super-middleweight when he beat Rocky Fielding in 2018.
The 29-year-old has since beaten American Daniel Jacobs and moved up to light-heavyweight to impressively stop Sergey Kovalev in November.
He has made no secret of his desire to set records in Mexico's already rich fighting history and a victory would ensure he can be called a four-weight world champion.
Often cited as one of the finest pound-for-pound fighters in the sport, Alvarez made his professional debut aged 15 in 2005.
During his career he has also beaten the likes of Gennady Golovkin, Amir Khan, Liam Smith and Miguel Cotto, and will start a heavy favourite when an agreement is finalised in the coming days.