Gatlin said on Instagram that he was “shocked and surprised to learn that my coach would have anything to do with even the appearance of these current accusations. I fired him as soon as I found out about this”.
The Athletics Integrity Unit says it is investigating the allegations published in Tuesday’s Daily Telegraph. IAAF President Sebastian Coe says “these allegations are extremely serious”.
The Telegraph reported that Mitchell and a track agent, Robert Wagner, offered to supply and administer testosterone and human growth hormone for an actor training for a film, for a fee of $250,000 (£187,000).
Gatlin, who also won the 100 metres at the 2004 Athens Olympics, has served two doping bans in his career.
Undercover reporters from the Telegraph filmed Mitchell and Wagner who have both denied wrong-doing.
“I am not using and have not used PEDs [performance-enhancing drugs],” wrote Gatlin on Instagram.
“I was shocked and surprised to learn that my coach would have anything to do with even the appearance of these current accusations. I fired him as soon as I found out about this.
“All legal options are on the table and I will not allow others to lie about me like this.
“I have no further comments as it is now a legal matter. They will next hear from my lawyer.”
According to the newspaper, its reporters visited Gatlin’s Florida training camp and Mitchell and Wagner offered to obtain and administer human growth hormone and testosterone for $250,000. The drugs, it is claimed in the report, would have been sourced from a doctor in Austria.
Perhaps even more damaging for athletics in general, though, are the secret recordings of Mitchell and Wagner claiming that doping is still widespread in the sport.
The United States Anti-Doping Agency (USADA) and the Athletics Integrity Unit (AIU), the new body set up by athletics’ world governing body the IAAF to oversee all anti-doping matters in the sport, are investigating the allegations.
In a statement sent to Press Association Sport, USADA said: “Investigations stemming from tips and whistleblowers play a critical role in anti-doping efforts.
“We are presently coordinating with the Athletics Integrity Unit in order to investigate these claims fully. As with all investigations, we encourage individuals with information to come forward as an important tool to help protect clean athletes.
“Importantly, individuals are innocent unless and until the established process determines otherwise. It’s only fair to let due process occur before jumping to any conclusions.”
AIU boss Brett Clothier told Press Association Sport: “These allegations are very serious and strike at the heart of the integrity of athletics.
“The IAAF anti-doping code and code of conduct applies not just to athletes, but also athlete support personnel. The Athletics Integrity Unit will be investigating this matter in co-operation with USADA and we hope the Daily Telegraph will provide information to assist.
“The use of new methodologies and designer drugs has always been a challenge for the anti-doping movement and this continues to this day. In this era, we understand that we cannot rely on testing alone to defend the sport against doping and so the AIU is both building its investigations and intelligence capability and implementing an intelligence based re-testing policy to meet such challenges.”
Gatlin won 100m gold at the World Championships in London this summer, triumphing over Usain Bolt.
His victory was greeted by boos from the crowd - a response he has become used to after serving bans for testing positive for a banned amphetamine and testosterone. Gatlin has always denied deliberately doping.
Both Mitchell, an Olympic sprint relay champion who also served a two-year doping ban during his track career, and Wagner have strenuously denied committing any offences relating to the newspaper investigation. Wagner said that he “played along”.
The Telegraph added that Gatlin’s long-term agent Renaldo Nehemiah had said Wagner had worked for Gatlin on no more than two or three occasions and the sprinter was not present when banned substances were discussed with either the agent or coach.