Joshua’s promoter, Eddie Hearn, has said a rematch between Anthony Joshua and Andy Ruiz Jr will take place in November or December this year.
Ruiz produced one of the biggest upsets in heavyweight boxing history to take Joshua’s IBF, WBO and WBA world heavyweight titles in New York on Saturday.
A rematch clause was part of the contract for the fight and Hearn says the clause had been triggered on Tuesday after talks.
British fighter Joshua was floored four times as American-born Mexican, Ruiz defied his underdog status to win in seven rounds at Madison Square Garden.
The London 2012 Olympic champion subsequently had a concussion test after the first defeat of his 23-fight career.