Agassi revealed in his recent autobiography that he used crystal meth in 1997 and failed a drug test, a result he says was thrown out after he lied by claiming he "unwittingly" took the illegal substance.
However, Helfant said there was no way to sanction the American retroactively since he has retired from tennis.
"There has been a lot of speculation about whether the ATP would reopen the case, but we cannot do that because he's no longer playing on the tour," Helfant said at the ATP World Tour Finals in London. "I asked an outside law firm to go through the records from 1997 so I had all the facts. Andre Agassi has admitted he failed a drugs test in 1997 and regrettably he then lied about it. Even more regrettably he got away with it."
He said the ATP's decision not to reveal the positive test was in line with its policy not to comment on doping cases.
"If we had revealed that test it would have been in contravention of the rules at the time," he said.
Helfant said he had a "very frank conversation" with Agassi after the book came out, and that the ATP has responded to the World Anti-Doping Agency's questions about the case.
"But what was said will remain between us and will not be made public," he said.
Agassi upset by Navratilova’s criticismsMartinez in Tamudo hint
