Tennis star Maria Sharapova announced Monday afternoon that she failed a drug test at the Australian Open.

During a news conference in Los Angeles, Sharapova, a five-time Grand Slam champion currently working through injuries, said she was informed by the International Tennis Federation that she tested positive for meldonium. The substance was just added to the World Anti-Doping Agency’s list of banned substances this year.

The ITF said in a statement that “Sharapova will be provisionally suspended with effect from [March 12], pending determination of the case.”

Sharapova, 28, said she started taking the substance in 2006 for magnesium deficiency and irregular EKG results, while also citing a family history of diabetes.

“It made me healthy, that’s why I continued to take it,” she said.

A former world No. 1, Sharapova has struggled with injuries recently. She withdrew from last season’s U.S. Open with a lingering right leg injury, and withdrew from several tournaments this year citing a left forearm injury.

Currently ranked No. 7 in the world, Sharapova has only played at one tournament this year – a quarterfinal appearance at the Australian Open where she lost to eventual finalist Serena Williams.

Sharapova offered an apology during her news conference.

“I made a huge mistake,” she said. “I let the sport down. I let my fans down.”

She fueled rumor talk on Sunday when her agent said a “major announcement” was on the way, but Sharapova is hoping that her career isn’t over yet.

“I know I face consequences and I didn’t want to end my career this way,” she said. “I hope I will be given the chance to play this game again.”

Nike suspended its business relationship with Sharapova after her admission Monday afternoon. The company announced its decision to “suspend our relationship with Maria while the investigation continues” in a statement released Monday night.