The boxing promoter, who represents Joshua, said he would announce a new opponent for AJ's Madison Square Garden bout at some point next week, with Miller denied a license for the fight by the New York State Athletic Commission on Wednesday.
Initial reports from ESPN on Friday claimed Miller, nicknamed ‘Big Baby’, had tested positive for a second banned substance in a VADA test, having already returned an adverse finding in a previous test taken on March 20.
Hearn then appeared to confirm the news on Twitter. He said: “We have now received news from VADA that Jarrell Miller has now failed a second seperate test for a further substance.
“AJ’s June 1 opponent will be announced next week - if you don’t think you can beat him clean then delete my number!”
Miller denies ever knowingly taking a banned substance. He wrote on Instagram on Thursday: "I am absolutely devastated upon hearing the news my boxing license has been revoked in NY State and I will be vigorously appealing this decision. I have NEVER knowingly taken any banned substance and when I found out the news last night I was totally shocked.
"My team and I stand for integrity, decency & honesty and together we will stand to fight this with everything we have!"
Hearn is already believed to have begun work on finding a new opponent for Joshua’s first fight outside the UK, with Cuban veteran Luis Ortiz, Polish-American Adam Kownacki, Bulgarian Kubrat Pulev, Mahmoud Charr and lesser-known US heavyweight Michael Hunter all listed as possible candidates.