Daniel Jacobs is moving up to super-middleweight to take on Julio Cesar Chavez Jr on December 20.
Jacobs will be back in action before the end of the year following his defeat to Saul 'Canelo' Alvarez in a middleweight unification bout in May.
After coming out on the wrong side of a points decision to relinquish his IBF title in Las Vegas, the 'Miracle Man' has decided to continue his career at 168 pounds as he aims to become a two-weight world champion.
His first fight in the new division will be against the experienced Chavez Jr, another former title holder at middleweight who also has a points defeat to Alvarez on his 56-fight record.
"I am thrilled to be making my debut at super-middleweight on December 20 against Julio Cesar Chavez," said Jacobs in a press release from promoters Matchroom.
"I've achieved a dream of becoming a world champion at middleweight and now I am seeking to secure my legacy by becoming a two-weight world champion.
"There are some great fighters and champions at 168 pounds and I believe that I will be a different beast up at super-middleweight.
"Facing Julio is a great test for my first fight, he's a former middleweight champion like me and he has the same goal as I do - Julio is always in great fights and I am sure that our styles will gel to be a thriller for the fans, and I plan to announce my arrival at 168 pounds in style."
Mexican Chavez Jr - son of the legendary Julio Cesar Chavez - has fought just once since losing to Canelo in 2017, stopping Evert Bravo inside a round on August 10.
"Going against Daniel Jacobs is the perfect fight for me because there is so much on the line," said Chavez Jr. "A victory gets me one step closer to a world championship and I’m not going to let anyone stand in my way.
"I know that Danny Jacobs is a former world champion and is a strong fighter with very good boxing skills. Those are the kind of boxers that bring out the best in me."
The bout will take place at Talking Stick Resort Arena in Phoenix.