Also, Swiss watchmaker Tag Heuer cut its ties with the tennis star.

Nike said it was “saddened and surprised” at her admission that she tested positive for a banned substance at the Australian Open in January.

Ms Sharapova said she had been taking meldonium since 2006, on the advice of her family doctor.

Nike ‘monitoring situation’

Her relationship with Nike dates back to when she was 11 years old.

“We have decided to suspend our relationship with Maria while the investigation continues,” Nike said.

“We will continue to monitor the situation.”

In 2010, the 28-year-old Russian tennis player signed a new eight-year contract with the US sportswear giant worth $70m (£49m) as well as a cut on sales of her own branded clothes.

Tag Heuer was in talks to extend its deal with Ms Sharapova, which ran out at the end of last year.

However, Tag Heuer said those talks have now been suspended and the company has decided not to renew the contract.

Sponsors ‘burned’

Ms Sharapova is the world’s highest paid female athlete after earning nearly $30m in 2015 from winnings and endorsements, according to Forbes. These include contracts with Evian, Tag Heuer, Porsche.

In 2014, Porsche named her as its first female ambassador.

Ms Sharapova, who lives in Florida, is also the face of Avon perfume Luck.

Paul Swangaurd, from the Warsaw Sports Marketing Center at the University of Oregon, said Nike’s decision reflected a “new era” for the way sponsors deal with these issues.

Nike is taking a “very proactive approach”, which resulted from “them being burned by a lot of athletes over the years, and growing impatient with putting so much investment behind athletes that potentially comes back to bite them in the court of public opinion”.

Last month, Nike dropped Manny Pacquiao after the boxer said homosexual people were “worse than animals”.

The company also severed ties with cyclist and drugs cheat Lance Armstrong as well as athlete Oscar Pistorius, who killed his girlfriend.

Failed test

Ms Sharapova tested positive for meldonium, a substance she said she had been taking since 2006 for health issues.

The International Tennis Federation (ITF) said she would be provisionally suspended from 12 March.

Ms Sharapova said: “I did fail the test and take full responsibility for it.”

She said she had taken meldonium after being given it by her family doctor and had known the drug by the name mildronate.

“A few days ago, after I received a letter from the ITF, I found out it also has another name of meldonium, which I did not know,” she said.

Source: BBC