Tennis star, Maria Sharapova tests positive to banned drug, faces 4-year ban.

Former tennis world number one Maria Sharapova said on Monday that she recently received a letter saying she had failed a drug test at the Australian Open.

The 28-year-old Russian, a five-times grand slam champion, has not competed since she lost to Serena Williams in the quarter-finals of the Australian Open in January and has struggled with a series of injuries in recent years.

She tested positive to Meldonium, also known as mildronate, is a Latvian-manufactured drug popular for fighting heart disease in former Soviet Union countries.

The drug was added to WADA's banned list because there was 'evidence of its use by athletes with the intention of enhancing performance.'

Several athletes have tested positive for the drug since it became illegal in January, including two Ukrainian biathletes and Russian cyclist Eduard Vorganov.

According to Oliver Brown, the Chief Sports feature writer, at The Daily Telegraph, Sharapova faces four-year ban if she is found to have taken meldonium intentionally to enhance performance. Two years if unintentional.