Jarrell Miller denied ever knowingly using a banned substance as he confirmed he intended to appeal the revoking of his boxing license.
The American (23-0-1) was due to face WBA, IBF and WBO heavyweight champion Anthony Joshua at Madison Square Garden on June 1.
However, that fight is in doubt after Miller returned an "adverse finding" to a test conducted last month.
Miller, 30, broke his silence Wednesday on Instagram, saying he planned to appeal the decision to revoke him of his license, while also denying wrongdoing.
"I want to thank all of my supporters who have stood by me since day one and especially during this extremely difficult time," he wrote.
"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"I am absolutely devastated upon hearing the news my boxing license has been revoked in NY State and I will be vigorously appealing this decision.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 & 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 vindicate [sic]. I don't have anything to hide and the truth will make itself known."