Britain's Lee Haskins took the IBF world bantamweight title as Randy Caballero failed to make the weight for their fight on Saturday.
Caballero, 25, was stripped of the belt after coming in five and a half pounds overweight for the Las Vegas contest.
The American, unbeaten in 22 fights, has been out of the ring for more than a year because of an ankle injury.
Bristol's Haskins, 32, turned down a request for the fighters to meet in a catch-weight contest.
"It's a strange one to process," Haskins' manager Jamie Sanigar told Boxing News.
"Lee was disappointed when I told him what was happening. I told him the fight was off but then in the next sentence I'm telling him he's a world champion."
The fight was last month added to the undercard of the WBC middleweight title contest between Miguel Cotto and Saul Alvarez.
It is yet to be decided if Haskins, who claimed the interim title earlier in the year with victory over Japan's Ryosuke Iwasa, will keep his full purse.