The failed drugs test of former world tennis number one Maria Sharapova was "reckless beyond description", according to former World Anti-Doping Agency president Dick Pound.
Sharapova, revealed yesterday she tested positive for the banned substance meldonium in January.
A number of sponsors have already distanced themselves from the Russian five-time Grand Slam winner.
Pound said running a multi-million dollar business depended on her being eligible to play tennis.
"There must have been a doctor following this," he told the BBC.
Meldonium, which Sharapova said she has taken since 2006 for health reasons, became a banned substance at the start of the year.
Meldonium is now on the banned list now because Wada started seeing it in lots of samples and found it does have performance-enhancing properties.
"You are taking something on a list. I am sorry, that is a big mistake - of course she should have known," said Pound, who was head of Wada from 1999 to 2007.
"She is taking something that is not generally permitted in her country of residence [USA] for medical purposes, so she says, so there must be a doctor following this.
"Anytime there is a change to the list, notice is given on 30 September prior to the change. You have October, November, December to get off what you are doing.
"All the tennis players were given notification of it and she has a medical team somewhere. That is reckless beyond description."
The ability to increase oxygen movement to muscles has seen meldonium used as a supplement for athletes, as it could have a positive affect on stamina and endurance.
"A drug like this over a long period of time is contraindicated. It means you would not take it over a long period of time. That is why there was an urge to put the drug on the list. A lot of people were taking it for performance enhancing.
"Most of the drugs of choice for dopers were built for therapeutic reasons - like EPO and others. That was supposed to regenerate blood if you had cancer treatment or surgical intervention if you needed to increase blood supply.
"Someone has said: 'Hmm, more oxygen in the blood? Hmm, very interesting. Let's see if we can use it for that purpose.'
The International Tennis Federation said Sharapova will be provisionally suspended from 12 March and faces a ban of up to four years.
"We have now increased the basic penalty for a first offence from two to four years," added 73-year-old Pound.
"If there is absolutely zero fault on the part of the athlete, where you can get a reduction of half of that suspension period, you are looking at a couple of years.
"That is for the tennis association to propose. If Wada does not agree, it will appeal to the Court of Arbitration for Sport for an increase," said Pound.