Jarrell Miller has denied "knowingly" taking a banned substance after he recorded an "adverse finding" in a drug test ahead of his world heavyweight title fight with Anthony Joshua.
Miller has been denied a licence by the New York State Athletic Commission to fight IBF, WBA and WBO champion Joshua on June 1 at Madison Square Garden in New York, live on Sky Sports Box Office.
The Brooklyn native plans to appeal the decision.
He said on Instragram: "I want to thank all of my supporters who have stood by me since day one and especially during this extremely difficult time.
"I have not been tuned in to social media and any other media outlets to focus and channel all of my energies into working hard with no distractions.
"I am absolutely devastated upon hearing the news my boxing license has been revoked in NY State and I will be vigorously appealing this decision.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 and honesty and together we will stand to fight this with everything we have!
"This was a voluntarily test that I was very happy to do and these results came just one week after another voluntarily test that I had taken which was completely clean. I refuse to just lie down and let my dream be taken away from me when I know in my heart that I've done nothing wrong.
"15 years of hard work. I'm WARRIOR .. I don't need a banned substance.
"Remember don't believe everything you hear and see. The facts will prevail and I shall be vindicated. I don't have anything to hide and the truth will make itself known."
Miller will be able to reapply if his B sample does not show an adverse finding but Joshua's promoter Eddie Hearn has said that they are likely to need a new opponent.
Earlier on Wednesday, Hearn said on Twitter of the Voluntary Anti-Doping Association (VADA) test: "We have been informed by VADA that there has been an adverse finding in Jarrell Miller's sample collected on March 20, 2019.
"We are working with all relevant parties and will update with more details soon.
"AJ's preparation continues for June 1 at MSG."