Evander Holyfield and Pittsburgh Steelers doctor Richard Rydze have denied any wrongdoing in the latest drugs scandal to hit American sport.
Holyfield said he was "disappointed" by the allegations
Federal agents have launched a major investigation into the internet sale of steroids and human growth hormone.
Reports alleging that he was an online customer forced ex-world heavyweight champion Holyfield to say: "I do not use and have never used steroids."
Rydze said purchases by him were for elderly patients and not sportsmen.
Rydze, the 1972 Olympic platform diving silver medallist, was identified as having used a personal credit card to buy human growth hormone to the value of $150,000 (£76,000).
He told Sports Illustrated magazine that Steelers' owners the Rooney family were aware of his activities away from his work with the team.
It's a practice that has nothing to do with me or what I stand for
Evander Holyfield denies using illegal performance-boosting products
"The Rooneys are aware that I do this," he said. "They have trust I would never do this with an athlete."
In a statement, Steelers president Art Rooney II said: "There is no evidence that Dr Rydze prescribed or provided any hormone treatments to any of our players.
"He has assured me that this has never happened and will never happen.
"We will continue to monitor this situation to make sure that we can continue to feel confident in our medical staff in this area."
Holyfield, 44, who has returned to the ring in a bid to claim a fifth world title, is denying allegations that he bought steroids from a company in Alabama.
He said the authorities were investigating "a practice that has nothing to do with me or what I stand for".
Holyfield was suspended by the New York State Athletic Commission in 2004 after a poor performance, and was urged by boxing pundits to quit.
But he decided to ignore their advice, and other states have licensed him to fight on.
His next bout is on 17 March against fellow American Vinny Maddalone at Corpus Christi in Texas.