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The tennis world just does not know what to make of it. Maria Sharapova, one of the game's most high-profile icons, admitted to failing a drug test at the Australian Open this year.

The details are still sketchy – she admitted to testing positive for meldonium, a substance she claimed she had been taking for over a decade, but which had only recently been included in the World Anti-Doping Agency's list of banned substances.

Her defence? She was not aware that meldonium had been added to the list.

The reactions have been mixed. Jennifer Capriati, a former American tennis player who had her own problems with illegal substances, went on a furious rant, calling for all her titles to be stripped. In contrast, another former tennis great, Martina Navratilova, was much more measured.

The furore over Sharapova can be explained because of the sheer impact she has had on the game. A 17-year old Sharapova burst onto the scene in 2004 when she defeated Serena Williams in the final of the Wimbledon, causing one of the biggest upsets of recent memory (video above).

Sharapova went on to win the French Open in 2006 and Australian Open in 2008, and also rose to World No. 1 on five separate occasions. However, injuries on various occasions meant she spent much of her time on the recovery table.

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Sharapova's footprint goes beyond tennis. Her success made her the golden girl of endorsements. From 2006 onward, she has been at or near the top of the list of highest-paid female athletes. Over the years, she has endorsed brands as varied as Motorola, Land Rover, Canon, Tag Heur and Tiffany.

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Immediately after the news of Sharapova's confession broke, apparel giant Nike announced that it was suspending its relationship with the Russian tennis star. The news was significant because Sharapova had been involved in a decade-long collaboration with Nike, even launching her own tennis clothing apparel line in collaboration with Nike. In 2010, Nike renewed their contract with Sharapova for $70 million, reputed to be the most lucrative ever deal for a sportswoman.

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