Porsche has postponed its planned activities with tennis star Maria Sharapova as the Russian continues to feel the ramifications of her failed drugs test.

The five-time grand slam champion revealed at a news conference on Monday that she tested positive for Meldonium at January's Australian Open.

Sharapova claimed she had been taking the drug for the past 10 years due to health reasons and was unaware it had been added to the World Anti-Doping Agency's list of prohibited substances as of January 1 this year.

Sportswear giant Nike subsequently suspended its sponsorship deal with Sharapova while the investigation continues and Swiss watchmaker TAG Heuer said it will postpone negotiations over renewing its contract with Sharapova, which ended on December 31.

Forbes magazine reported that Sharapova earned $29.5million last year, with the bulk of that sum coming via endorsements, and she is now further counting the cost of her failed test following Porches' announcement.

A Porsche statement read: "We are saddened by the recent news announced by Maria Sharapova. Until further details are released and we can analyse the situation, we have chosen to postpone planned activities [with Sharapova]."