Nike said it was suspending ties while the case is being investigated.
She was informed by the International Tennis Federation (ITF) that she tested positive for Meldonium, which was added to the World Anti-Doping Agency’s list of banned substances on 1 January this year.
Sharapova said she has legally been taking the drug for the past 10 years.
“We are saddened and surprised by the news about Maria Sharapova,” Nike said in a statement.
“We have decided to suspend our relationship with Maria while the investigation continues. We will continue to monitor the situation.”
The 28-year-old five-time grand slam champion will be provisionally suspended starting 12 March, the ITF said.
She is the seventh athlete in a month to test positive for meldonium, which is used to treat diabetes and low magnesium.
“I made a huge mistake. I let my fans down and I let the sport down,” said Sharapova, a teenage tennis prodigy who became the third-youngest Wimbledon champion.
“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,” she told a news conference in a downtown Los Angeles hotel.
