Lamont Peterson's publicist Andre Johnson has insisted that the American is not a "cheater".
Peterson's world title showdown with Amir Khan on May 19 in Las Vegas has been called off after he tested positive for a banned steroid.
Peterson, who won the WBA and IBF titles in controversial fashion from Khan in December, now faces an anxious wait over what further action could be taken against him.
However Johnson insisted the 28-year-old had done nothing wrong and would fight to clear his name.
He told Sky Sports: "Lamont Peterson has been boxing for 18 years. In 18 years, barring this incident, he's never tested positive for anything - and after this incident. Three other tests were taken that he tested negative for.
"We're going to get to the bottom of this and do everything in our power to clear Lamont's name. Lamont will be fighting very soon.
"We're extremely disappointed. We wanted to make this fight happen. We're sorry it didn't happen.
"Lamont is not a cheat. He is not a steroid abuser. There's no evidence of anabolic steroid abuse in his body or in his system. The doctor that saw him in Nevada determined he has low testosterone levels. There's no way a guy with his type of level can test positive for an anabolic steroid that is testosterone-based.
"Lamont did nothing wrong. He's not a doper. He's not a cheater.
"He's distraught. He wanted to clear his name and do what he was born to do - fight.
"Mark my words: Lamont Peterson is a man of tremendous character - he's a fighter. We will fight to get the truth."
On the possibility of a future rematch against Khan, Johnson said: "We would love to fight Amir Khan again. That's going to be up to Amir Khan.
"We don't have a problem. We would love to make it happen. That's why he accepted the opportunity to fight him this time - because the fans wanted it."
