World Anti-Doping Agency chairman Dick Pound has suggested Greg Rusedski's drugs case should be reopened.
British number two Rusedski has always protested his innocence
The British number two was cleared following his positive test for nandrolone by an Association of Tennis Professionals-appointed tribunal.
But Pound said the ATP might want to "seek a further explanation" when a Wada report into the nandrolone outbreak in tennis is released.
The ATP asked Wada to investigate after more than 50 high readings of the drug.
Pound told the Observer newspaper that he "always thought Rusedski was trying to get lost in the crowd".
The Wada chairman said he believed it was impossible Rusedski would have been unaware of the need to avoid possible sources of nandrolone.
The string of elevated readings was first blamed on contaminated supplements but suspicion has since fallen on electrolytes, or salt tablets, supplied by the ATP.
Pound, who believes both theories are unfounded, added: "This is not a 12-year-old told to go to bed on time.
"This is a 30-year-old professional tennis player who is clearly aware of all these cases, yet persists with the behaviour that led to the positive tests and then says 'well, you didn't tell me'. It defies imagination.
"So far as I am aware there's not the slightest bit of evidence that the electrolytes were tainted.
"If we were to conclude that the hypothesis is completely unsubstantiated, then they [the ATP] may very well say 'well, maybe we should seek a further explanation'."
As for the impending Wada report into the spate of positive tests, Pound said "he would hope" the ATP would act upon it, though the organisation has no legal powers to force a review.
Seven players' readings were high enough for them to fail tests for the banned performance-enhancing steroid in 2003.
They were subsequently exonerated, but Pound said that should have no bearing on Rusedski's case.
"The fact you may have shot yourself in the foot on a previous occasion doesn't compel you to do the same thing in a different case.
"The cases were not similar. The only thing that was similar was that there was a positive test for nadrolone"
Rusedski, 30, who was facing a two-year ban and the likely end of his career if found guilty, has yet to decide whether to seek damages from the ATP.