Callum Smith will face an opponent who has lost to one of boxing’s unbeaten light heavyweight champions in Smith’s debut at the 175-pound limit.

BoxingScene.com has learned Smith and Lenin Castillo have agreed to fight September 25 in London. The Smith-Castillo clash will be part of the Anthony Joshua-Oleksandr Usyk undercard at Tottenham Hotspur Stadium and is expected to be broadcast by Sky Sports Box Office during a pay-per-view broadcast in the United Kingdom and Ireland.

It hadn’t been determined at the time this story was posted if the bout between Smith (27-1, 19 KOs) and Castillo (21-3-1, 16 KOs) will be a 10-round fight or a 12-round WBC elimination match.

Regardless, Liverpool’s Smith will fight for the first time since he lost his WBA super middleweight title to Canelo Alvarez on December 19 at Alamodome in San Antonio. Mexico’s Alvarez dominated Smith during their 12-round, 168-pound championship match and won by big margins on all three scorecards (119-109, 119-109, 117-111).

The 31-year-old Smith took the biggest fight of his career on barely four weeks’ notice.

The 32-year-old Castillo competed more recently than Smith. He stopped Ronald Gonzalez (8-1, 8 KOs) after the fourth round of their scheduled 10-rounder July 21 in Santo Domingo, Dominican Republic.

Venezuela’s Gonzalez suffered an undisclosed injury during the first round and couldn’t answer the bell for the fifth round.

Castillo’s victory over Gonzalez marked his return from a 21-month layoff following his lopsided loss to WBA light heavyweight champion Dmitry Bivol.

Russia’s Bivol (18-0, 11 KOs) easily out-boxed Castillo throughout their 12-round title bout in October 2019 at Wintrust Arena in Chicago. Bivol beat Castillo by scores of 120-107, 119-108 and 119-108.

Santo Domingo’s Castillo previously lost to a 10-round unanimous decision to light heavyweight contender Marcus Browne (24-1, 16 KOs) and an eight-round majority decision to Joseph Williams (13-0, 8 KOs).

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.