Former World Anti-Doping Agency chief Dick Pound said Tuesday that Maria Sharapova was "reckless beyond description," as the Russian tennis star faces an uncertain future in the sport after failing a drug test at the Australian Open.

Sharapova revealed Monday she had failed a test for meldonium, a substance she had been taking legally taken for 10 years to deal with health issues, such as an irregular heartbeat and a history of diabetes in her family.

But meldonium was added to the WADA banned list at the start of 2016 because of "evidence of its use by athletes with the intention of enhancing performance."

Pound said he could not fathom how Sharapova allowed herself to be in this situation given the high stakes involved, both professionally and financially.

"Running a $30 million business depends on you staying eligible to play tennis. You are taking something on a list, which you have known about for four months. I am sorry, that is a big mistake -- of course she should have known," Pound said in an interview with BBC Sport.

"She is taking something that is not generally permitted in her country of residence [the United States] for medical purposes, so she says, so there must be a doctor following this."

Sharapova, 28, is waiting to hear what sanctions she will face from the International Tennis Federation, which informed her of the positive test on March 2 and confirmed she would be provisionally suspended from March 12 pending an independent tribunal to hear the case.

Sharapova faces a ban of up to four years, but could receive some leniency if she can prove she needed to take the drug for medical purposes.

She said she had not read the updated list of banned substances sent to athletes in December and took "full responsibility" for her actions.

"Any time 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," Pound told BBC Sport. "All the tennis players were given notification of it and she has a medical team somewhere. That is reckless beyond description."

Sharapova will also face a battle to win back lucrative endorsement contracts.

According to Forbes, Sharapova earned some £21 million ($30 million) in 2015, making her the highest-earning female athlete in the world for the past 11 years, with her off-court endorsements dwarfing her income from prize money.

After the news broke, three major sponsors -- sportswear giant Nike, watchmaker Tag Heuer and luxury car brand Porsche -- all distanced themselves from the tennis superstar.