The WBO and WBA number one contender stated on Thursday he would stand in the way of Joshua potentially fighting Deontay Wilder in an undisputed unification and Ryabinskiy has confirmed this is now the case.
As a result, Joshua has just a few months to defend his title against the Russian and less than a month to begin negotiations.
Povetkin’s wishes mean bad news for Wilder’s hopes of a massive heavyweight battle.
Ryabinskiy said: “Povetkin is now a mandatory contender to Anthony Joshua.
“He was appointed by WBA. Now there are 150 days to arrange the fight, it must take place.
“Before the fight with Sasha, Joshua has no right to fight with anybody else. We have 30 days to negotiate,” he added.
Speaking through World of Boxing Russia on Thursday, Povetkin had stated: “I’m the mandatory challenger for Joshua. I look forward to the moment when I can compete against the best in the world.
“Anthony has four belts. I want this fight and I don’t even think about fighting someone else.”
It still remains a possibility that Joshua’s promoter Eddie Hearn could ask for special dispensation to secure the first battle for every recognized top division belt since 1999 when Lennox Lewis defeated Evander Holyfield as this contest with Wilder would be of significance to the whole of boxing.
Whether the WBA would be on board is another matter, although President Gilbert Mendoza does have a reputation for being one of the more lenient heads of the organizations.
Wilder will have to hope this is the case as Joshua will have to face Povetkin or lose at least one of his championships moving forward
Phil Jay is Editor of World Boxing News. Follow on Twitter @PhilDJay