0716 GMT August 24, 2019
Joshua lost his IBF, WBA and WBO belts to Ruiz Jr. in New York City and immediately invoked his rematch clause, but the location of a second fight has been a sticking point, Sky Sports reported.
A return to Madison Square Garden was mooted, and Cardiff's Principality Stadium was also considered.
Mexico, the country of Ruiz Jr.'s heritage and where the new champion called for to host the rematch, was never a serious candidate.
Saudi Arabia has now emerged an option to host Joshua's challenge for Ruiz Jr.'s titles, expected in December.
Last year, the country held the World Boxing Super Series final when Callum Smith knocked out George Groves.
More recently, Amir Khan defeated Billy Dib in Saudi Arabia, with Hughie Fury's win over Samuel Peter on the undercard.