Maria Sharapova has revealed that she failed a drugs test at the most recent Australian Open.

News broke last night that the 28-year-old had called an unscheduled press conference in Los Angeles, where many had tipped the Russian to announce her retirement.

However, the five-time Grand Slam champion sparked a surprise this evening when she confirmed that she had tested positive for a banned substance at the first major event of the year.

Addressing the gathered media, Sharapova insisted that she had been taking a medicine prescribed by her doctor for the past decade that was not included on the World Anti-Doping Agency's list of performance-enhancing substances.

However, it was then added on January 1, 2016 - something that the right-hander had failed to check.

"I received a letter on December 22 from WADA for the changes next year and where the tests will be with a link to the changes for 2016. I did not look at that list," she admitted. "I failed the test and take full responsibility for that."

The world number seven was unable to provide any details regarding a potential ban, although she did stress that she hoped to play again, rather than be forced into retirement.

Sharapova first made the headlines in 2004 when aged 17 she became the third-youngest woman to win Wimbledon.