Madrid - Rafael Nadal said on Thursday he was shocked that the ATP did not take action regarding Andre Agassi's admission that he took drugs in 1997 but lied about the circumstances to avoid a ban.
"If the ATP covered for Agassi at the time then I think that's dreadful," Nadal said in Madrid as he prepared to receive a civic award.
"The only thing I can say is that if they covered at that moment for the player and punished others for doing the same kind of thing then that would seem to me to be a lack of respect for all sportsmen," the world number two said.
Agassi, one of just six men to have won all four Grand Slam titles and widely regarded as one of the sport's finest players, stunned the world when he revealed earlier this week he'd taken the highly-addictive drug crystal methamphetamine.
The American, now 39, also admitted that he lied to the governing body of the ATP to escape a ban.
On being told he had tested positive for the banned stimulant, Agassi said he wrote a letter to the ATP, the Association of Tennis Professionals, claiming he had taken it by accident and asking for leniency.
No disciplinary action was taken.
Since the story came to light, World Anti-Doping Agency (WADA) president John Fahey has asked ATP chiefs to "shed light" on the issue.
Crystal Meth is on WADA's List of Prohibited Substances and Methods.
The World Anti-Doping Code only took effect in 2004 and has an eight-year statute of limitations.
But Fahey said that WADA would expect the ATP, which administered its own anti-doping programme at that time, to shed light on the story.
Nadal concluded that "cheats have to be punished" and said he could not understand why Agassi "now that he is retired comes out and says this - it's a way of senselessly damaging the sport".