Promoter Eddie Hearn said Andy Ruiz Jr has signed to fight Anthony Joshua in Saudi Arabia despite speculation he has not committed to the bout.
The unified world heavyweight champion, 29, has not shared any fight details on social media since the 7 December rematch was announced on Friday.
His trainer Manny Robles says “there’s a reason why” Ruiz has kept silent.
Hearn, who promotes Joshua, said: “Both fighters signed for this fight. The governing bodies have been informed.”
At a London news conference where neither Joshua or Ruiz were present, Hearn said the rematch will take place in an open-air stadium in Diriyah, on the outskirts of Riyadh.
Omar Khalil, working for the Saudi agency delivering the event, said fans who purchase a ticket will automatically be issued a visa to visit the country.