Maria Sharapova was warned at least five times by tennis authorities that the drug meldonium had been banned in the month before she failed a doping test at the Australian Open.
In addition, Russia's athletics federation has said it had repeatedly warned athletes and coaches not to take meldonium.
Sharapova, 28, announced on Monday that she had been caught in a doping test after taking the drug, which became a banned substance in January.
The five-times Grand Slam winner claimed that it was an honest mistake, as she had taken the drug, sold as Mildronate in Russia, for ten years and had failed to notice that it had been banned.
However, three correspondences from the International Tennis Federation (ITF) and two from the Women's Tennis Association (WTA) were sent to players containing warnings that meldonium was to be banned, according to the Times.
In addition, the World Anti-Doping Agency had also give players notice of the new ban as early as September last year.
This followed a statement by the Russian athletics federation (ARAF) on Wendesday: "To the attention of sports people and coaches. The ARAF has on multiple occasions warned sports people, coaches, and support staff that, since January 1 this year meldonium is included in the list of the banned substances."
The announcement said on several occasions last year items were posted on the federation's website stating meldonium was banned, the message was also passed on at a conference of coaches last October and at three training camps.
Despite the scandal surrounding her, Sharapova was seen dressed head-to-toe in Nike gear and drove her Porsche to the supermarket on Wendesay - even though both brands suspended their relationship after her revelation.
She hit the gym in Los Angeles wearing black Nike leggings and a black Nike sweatshirt. The brand ended her most lucrative deal, an eight-year contract extended in 2010 for a reported $8.5 million a year, just hours after her announcement on Monday.
She looked relaxed and even smiled as she walked around, even though she has lost at least $14 million of sponsorship contracts in the past 24 hours and doesn't know yet how her career will be affected.
She then drove her Porsche to Whole Foods, this time wearing white Nike sneakers. Porsche, another one of her major partners, said that while they are "certainly not dumping" Sharapova, they are currently "not pursuing any further activities" with her. Her deal with Porsche was worth $2.8 million.
Swiss watch brand TAG Heuer followed suit, saying its contract with Sharapova had expired at the end of 2015 and it has pulled out of negotiations on a new agreement. The contract was also priced at $2.8 million.
Her other partners, Avon, Evian and Head, have yet to comment.
Sharapova said in her press conference that she was initially given meldonium in 2006 by her "family doctor" and kept taking it for a decade because of health issues such as a magnesium deficiency and a genetic disposition towards diabetes.
However, the drug which is mainly available in Eastern Europe is said to have become a drug of choice for Russian athletes implicated of cheating in other sports. It was regularly given to Soviet troops in the 1980s to boost their stamina.
Latvian manufacturers that make meldonium have now said that the substance is normally prescribed for medical use for four to six weeks - much shorter than Sharapova's course of treatment.
A Grindeks spokesman said: "Depending on the patient's health condition, treatment course of meldonium preparations may vary from four to six weeks. Treatment course can be repeated twice or thrice a year.
"Only physicians can follow and evaluate patient's health condition and state whether the patient should use meldonium for a longer period of time."
- Daily Mail