Canelo Alvarez has withdrawn from his scheduled rematch with middleweight world champion Gennady Golovkin.
Alvarez made the announcement on Tuesday in the wake of the Mexican's two positive tests for banned substance clenbuterol.
The eagerly-awaited bout was scheduled to take place on May 5 at the T-Mobile Arena in Las Vegas.
A hearing on Alvarez's failed tests - which he put down to eating contaminated beef in Mexico - is expected to take place on April 18.
Alvarez said: "I am truly shocked about what has happened and for those who have doubts and suspicions about my integrity I have always been and always will be clean fighter"
"I want to apologise to HBO, [my sponsors] Tecate and Hennessy and all my other sponsors, the media and to everyone who is involved in the promotion of this event and especially to the fans. I respect this sport. I will always be a clean fighter."
Golden Boy Promotions president Eric Gomez said: "It’s unlikely this matter will be resolved properly [by April 18], and obviously we need enough time to promote a fight of this magnitude."
The first fight between Alvarez and Golovkin ended in a controversial draw last September.