Worth an estimated $195 million, Sharapova will be unable to continue her work as a goodwill ambassador with the U.N. Development Program until the conclusion of the investigation into her admission that she tested positive for the banned substance meldonium at the Australian Open in January.

"The United Nations Development Programme (UNDP) remains grateful to Maria Sharapova for her support of our work, especially around the Chernobyl nuclear disaster recovery," said a UNDP spokesperson.

"However, in light of Ms. Sharapova's recent announcement, we last week suspended her role as a Goodwill Ambassador and any planned activities while the investigation continues. We wish Ms. Sharapova the best."

The 28-year-old, who was paid a symbolic $1 salary in her role, said at the time that it was one of her "proudest contracts ever."

Sharapova has worked with the program which aims to eradicate poverty and inequality for nearly a decade, focusing mainly on helping victims of the 1986 Chernobyl disaster.

She made a $100,000 donation to young survivors caught up in the world's worst nuclear accident upon her appointment in 2007.

Sharapova's family once lived 80 miles north of Chernobyl in the Belorussian city of Gomel and were forced to flee to Siberia because of fears over radiation after the accident.

According to U.N. guidelines, goodwill ambassadors are "persons of integrity" who "possess the personality and dignity required for such high-level representative capacity."

Sharapova appears to have contravened article 28 of Guidelines for the designation of Goodwill Ambassadors and Messengers of Peace, which states that the arrangement will be re-examined if the ambassador "engages in any activity incompatible with his/her status or with the purposes and principles of the U.N., or if the termination is in the interest of the organization."

Ranked as the highest earning female athlete in the world for the 11th year running in 2015 by Forbes, Sharapova's failed drug test admission has led to a number of companies reassessing their relationship with the Russian.

Nike, Tag Heuer and Porsche all suspended their sponsorship deals with Sharapova, though racket manufacturer Head has said it will extend her contract.

The five-time grand slam winner took to Facebook Saturday telling fans she was "determined to fight back."

Sharapova said she had been taking the heart drug since 2006 but dismissed reports she took it every day, saying she followed doctors' instructions and took it in the "low doses recommended."

Reports last week had suggested the normal course of treatment for patients on meldonium, sometimes known as mildronate, is four to six weeks.

"That headline has been repeated by many reporters who fail to tell their viewers and readers what the rest of the story says," wrote Sharapova on her Facebook page.

"The story quotes the manufacturer of my medicine as saying: '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.'

"That's exactly what I did. I didn't take the medicine every day."

Sharapova failed a drug test on January 26 after losing to Serena Williams in the Australian Open quarterfinals. She was charged with an anti-doping violation on March 2, and was provisionally banned from March 12.

The ban could be reduced to two years or less if anti-doping officials find Sharapova did not intentionally take the drug to enhance performance.

(CNN)