Soon after Peyton Manning announced his retirement from football on Monday, sports fans were wondering if another superstar would also be retiring: Tennis player Maria Sharapova planned a press conference to make a “major announcement.”

But instead, Sharapova announced that she failed a drug test for taking mildronate — also called meldonium — and was waiting to find out what her punishment will be. The drug is made in Latvia and used to treat ischemia, which is a lack of blood flow. It is not approved for use in the U.S. by the FDA.

During the press conference, she said she’s been taking the drug for 10 years because she was getting sick often, “and I had a magnesium deficiency. I also had an irregular EKG result, and I have a family history of diabetes.”

The National Center for Biotechnology Information (NCBI), a U.S. government-funded resource for molecular biology information, said this about the drug in a Dec. 2015 abstract:

“To date, substances such as Mildronate (Meldonium) are not on the radar of anti-doping laboratories as the compound is not explicitly classified as prohibited. However, the anti-ischemic drug Mildronate demonstrates an increase in endurance performance of athletes, improved rehabilitation after exercise, protection against stress, and enhanced activations of central nervous system (CNS) functions.”

Sharapova, who is 28 years old and currently ranked No. 7 in the world, said the drug was added to the banned substance list as of Jan. 1, 2016, but that she didn’t read a letter she received on Dec. 22, 2015, from WADA (the World Anti-Doping Agency) informing players of newly banned substances.

Sharapova's drug test: What's Meldonium?

After Sharapova spoke, the ITF issued a statement saying it can confirm the following:

On 26 January 2016, Ms Sharapova provided an anti-doping sample to the TADP in association with her participation in the 2016 Australian Open.

That sample was analysed by a World Anti-Doping Agency (WADA) accredited laboratory, which returned a positive for meldonium, which is a prohibited substance under the WADA Code and, therefore also the TADP.

In accordance with Article 8.1.1 of the TADP, Ms Sharapova was charged on 2 March with an Anti-Doping Rule Violation.

Ms Sharapova has accepted the finding of meldonium in her sample collected on 26 January.

As meldonium is a non-specified substance under the WADA (and, therefore, TADP) list of Prohibited Substances and Prohibited Methods, Ms Sharapova will be provisionally suspended with effect from 12 March, pending determination of the case.

“I made a huge mistake and I let my fans down and let the sport down that I’ve been playing since age 4 and that I love so deeply,” she said.

Also see: Peyton Manning hangs up cleats after 18 years as an NFL quarterback

Sharapova also acknowledged that before the press conference many people thought she might be announcing her retirement, and said, “If I was retiring, it wouldn’t be in a downtown Los Angeles hotel with this ugly carpet.”

The carpet is quite unseemly. Kevork Djansezian/Getty Images

Endorsements

It is still unclear how much time she might be forced to take off from the tour, but the response from some of her biggest sponsors was swift.

Sharapova has been the highest paid female athlete in the world for 11 years in a row, according to Forbes, which points out that she made nearly $30 million between June 2014 and June 2015. And since less than $7 million of that was from prize money, the bulk of it was from her sponsors, which include Nike NKE, -1.46% , Head, Tag Heuer, Porsche VOW, -3.20% , Evian DANOY, -0.07% and Avon US:AVP. She also started a candy company called Sugarpova in 2012, which has been very successful.

Already, Nike, Porsche and Tag Heuer have suspended or not renewed deals with Sharapova. Nike said the following in an emailed statement:

“We are saddened and surprised by the news about Maria Sharapova. We have decided to suspend our relationship with Maria while the investigation continues. We will continue to monitor the situation.” A picture of Sharapova remained on the company’s website as of Tuesday, for its NikeCourt line.

Also see: Maria Sharapova loses grip on millions of dollars as Nike leads sponsor exodus

Sharapova, who has been battling injuries for months, will also lose the roughly $298,000 that she won at the 2016 Australian Open, where she lost in the quarterfinals to Serena Williams. According to the ITF, a positive drug test at an event “automatically leads to disqualification of the results obtained by the player…including forfeiture of any medals, titles, ranking points, and prize money.”

Her playing career

Sharapova won Wimbledon at age 17 and became an instant star. She was born in Russia and moved to the U.S. when she was 7, but says she doesn’t plan to give up her Russian nationality.

On the court, she has won five Grand Slam titles — Wimbledon in 2004, the U.S. Open in 2006, the Australian Open in 2008, and the French Open in 2012 and 2014. Having won each of the major tournaments at least once, she is one of only six women to win the “career Grand Slam” in the Open era, which began in 1968.

“I don’t want to end my career this way, and I hope i’m given another chance to play this game,” she said in the press conference.

This story has been updated to include responses from some of Sharapova’s sponsors.