A deal for the two heavyweights was expected to be completed early this week with the Manchester Arena likely to stage the bout on December 10, but the plans could be scuppered should the WBA not allow the pair to fight for its version of the world crown.
Tyson Fury has vacated both that belt and the WBO title and while there appears to be no specific demand for the WBO strap to be on the line, Hearn has revealed that former unified champion Klitschko is keen to compete for WBA honours.
Hearn told Sky Sports News: "The deal is there but we are awaiting sanctioning from the WBA.
"Both teams have written to the WBA to request sanctioning of our fight, but Wladimir wants the WBA belt to be on the line so until that is approved we cannot move forward.
"We expect news in the next few days, but in the meantime I believe both sides will look at alternative options for December 10 while we hope to get the news we need to make the fight happen."
Joshua currently holds the IBF title, which would also be on the line should a deal be completed for the mega-fight to take place in the final month of 2016.