Jennifer Capriati took to Twitter today to express her disappointment at Maria Sharapova, who announced at a news conference that she had failed a drug test at the Australian Open.

Those tweets were part of a larger, rambling rant by the Tennis Hall of Famer today.

Other former players were more supportive of Sharapova.

"Hold your horses everyone - about Maria - I don't have all the facts, I hope it's an honest mistake, stuff was legal as far as I know till 2015," wrote American Great Martina Navratilova.

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Former player James Blake described Sharapova's response as "classy".

The 28-year-old, a five-time grand slam champion, will be provisionally suspended from March 12, the International Tennis Federation (ITF) said.

She is the seventh athlete in a month to test positive for meldonium, which is used to treat diabetes and low magnesium, and was only banned by the World Anti-Doping Agency (WADA) as of January 1.

"I made a huge mistake. I let my fans down and I let the sport down," the former world No.1 told a news conference.

"I take full responsibility for it.

"I know that with this I face consequences and I don't want to end my career this way. I really hope that I will be given another chance to play this game."

The ITF's anti-doping program calls for a four-year suspension for a positive test, but that ban can be reduced in various circumstances, such as for first-time offences or if the player shows no significant fault or negligence. If a player bears no fault or negligence, there is no suspension.

According to Forbes, she earned $US29.5 million ($A39.47 million) in 2015, mostly from endorsements.

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Sharapova said her family doctor had been giving her mildronate, which is also called meldonium, for 10 years after she frequently became sick, had irregular EKG results, a magnesium deficiency and a family history of diabetes.