Nike has suspended its contract with Maria Sharapova after the five-time grand slam winner announced she had failed a drug test. The 28-year-old Russian revealed on Monday that she had tested positive for meldonium following her quarter-final defeat against Serena Williams at the Australian Open in January. A statement from sportswear giant Nike read: “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.”

Watchmaker Tag Heuer has also decided not to renew its sponsorship contract with Sharapova, which ended on December 31 last year. “We had been in talks to extend our collaboration,” A statement from Tag Heuer, who had sponsored Sharapova since 2004, read. “In view of the current situation, the Swiss watch brand has suspended negotiations, and has decided not to renew the contract with Ms Sharapova.”

Meldonium, which Sharapova said she had legally taken throughout her career, was placed on the banned list by the World Anti-Doping Agency (WADA) at the beginning of the year following “evidence of its use by athletes with the intention of enhancing performance”. Sharapova claimed she did not realise the substance was illegal, but took “full responsibility” for her actions. The International Tennis Federation said Sharapova had been informed of the positive test on March 2 and she will be provisionally suspended from March 12.