LONDON (Reuters) - Anthony Joshua will try to regain his lost heavyweight titles in a rematch with Mexican-American Andy Ruiz Jr. in November or December at a location to be decided, promoter Eddie Hearn said on Tuesday.
Ruiz produced one of boxing's biggest upsets by beating the 29-year-old Briton with a seventh-round stoppage at New York's Madison Square Garden on Saturday.
Joshua, previously undefeated and fighting for the first time in the United States, was defending his IBF, WBA and WBO titles but was knocked down four times in the fight.
"We have today triggered the contracted rematch clause with Andy Ruiz Jnr," Hearn said on Twitter.
"The fight will take place in Nov/Dec at a venue to be confirmed shortly."
Hearn told reporters after the fight that a rematch was a 'must win' for the 2012 Olympic super-heavyweight champion.
(Reporting by Alan Baldwin, editing by Toby Davis)