The news broke on Monday that Klitschko suffered a setback in training last week meaning a potential unification clash was no longer available in 2016.
Despite this, Joshua will plough on with his fight in Manchester at the end of this year as Hearn plans to find a replacement opponent at short notice.
“We’ve been in deep negotiations for a few weeks now waiting on the decision from the WBA,” Hearn told Sky Sports.
“I was made aware that Wladimir picked up a minor injury late last week but regardless of that, with just over six weeks to go til December 10, it’s unrealistic to put together a fight of this magnitude and give it the full build-up it deserves.”
On Joshua v Klitschko going ahead at a later date, Hearn added: “There will be an official announcement on Joshua v Klitschko coming very soon but for now we are seeking a new foe for December 10 and building a huge card for Manchester.”
Eric Molina, Bryant Jennings, Kubrat Pulev and David Price now come back into play for Joshua for what will be the Londoner’s second defence of his world crown,
