ATP chairman Adam Helfant has confirmed the governing body will not be reinvestigating Andre Agassi's positive drugs test in 1997 and cannot impose retrospective sanctions.

The American stunned the tennis world with the revelation in his recent autobiography he failed a test for crystal meth and then lied about how it came to be in his body to avoid a ban.

The reaction from within the game has been mixed, with Andy Murray and Andy Roddick supporting their boyhood idol but Marat Safin calling for Agassi to give back his titles and prize money.

The ATP have also come in for criticism, including from the World Anti-Doping Agency, and Helfant, who revealed he had had a "very frank conversation" with the former world number one, admitted the episode has been "regrettable".

Speaking ahead of the Barclays ATP World Tour Finals, which begin at the O2 in London on Sunday, he said: "The ATP's policy is we don't comment on doping matters unless a doping violation is found and that will continue to be our policy but I thought some perspective was in order.

"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.

"In compliance with the ATP's anti-doping policy, no disclosure was made. If we had revealed that test it would have been in contravention of the rules at the time.

"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. We have responded to WADA but what was said will remain between us and will not be made public."

The ATP's current drugs policy has come under fire from the top players, notably Murray and Rafael Nadal, who feel WADA's 'whereabouts' rule - where athletes must make themselves available for testing every day throughout the year - is unfair.

The issue has hit the headlines again in the last week, with Belgian pair Xavier Malisse and Yanina Wickmayer being handed one-year bans after failing foul of the rule.

Helfant acknowledged there are issues and revealed the ATP are in discussions with WADA.

He said: "The whereabouts programme was originally meant for out-of-competition testing and it's a programme that's one size fits all.

"So the question is how should it be applied to a sport that's in competition nearly all the year? We are in conversation with WADA about the technical issues."

The length of the season also continues to be a major issue and the even later staging of this year's Tour Finals - being held in London for the first time - means the top players will have almost no time off before they begin training for the start of the new season in January.

British number one Murray will head out to his winter training base in Miami on December 6 while Nadal - the most outspoken critic of the tight schedule - is representing Spain in the Davis Cup final in two weeks' time.

"Everybody thinks the same," said the world number two. "We finish the year December 6 and then start the next season on January 1. That's the calendar and right now we are suffering.

"The ATP and the players are talking and we have got to work hard. Maybe not for us but for the next generations we can change things."

Helfant admitted there is no likelihood of the calendar changing radically in the near future.

"It's a nice problem to have but I'm definitely sympathetic to the view that our season is too long," he said. "We'll continue to talk to the players and see what we can do but I don't promise that there's an easy solution."