Joshua suffered a shock defeat to Ruiz Jr in New York over the weekend.
The Brit lost his WBA, WBO and IBF heavyweight belts as a result of the first defeat of his career.
Promoter Eddie Hearn cleverly wrote a rematch clause into the fight contract for if the worst was to happen.
But Ruiz Jr has another major problem in that the WBO are set to call a mandatory defence in September.
Mandatory fights are supposed to take precedent over any rematches.
Hearn claimed he would try to make Joshua vs Ruiz Jr 2 for either November or December.
But it is highly unlikely the Mexican will fight twice in three months.
So he may have to decide between defending the WBO belt or taking on Joshua for a mega-money showdown.
The two fighters who are in the best position to steal the WBO title are Dillian Whyte and Oleksandr Usyk.
Whyte is the No 1 ranked fighter with that governing body while Usyk is the unified cruiserweight champion.
As things stand, the power lies in the hands of Whyte, who can call a mandatory fight against Ruiz Jr.
However, Usyk will be given the shot ahead of Whyte if he wants it.
But the Ukrainian has never before fought at heavyweight so he would be risking his main shot at the title.
He was supposed to fight Carlos Takam but was forced to withdraw from the bout due to injury.
All parties involved could agree to allow Joshua vs Ruiz Jr to take place first.
But with such a glorious opportunity opening up for Whyte and Usyk, the power is in their hands.