Maria Sharapova

A five-time grand slam champion, Sharapova has struggled with injuries in recent years while she also served a 15-month ban after testing positive for meldonium at the 2016 Australian Open.

Announcing her decision to step away from the game in Vogue and Vanity Fair, she wrote: "How do you leave behind the only life you’ve ever known? 

It has been a troubled season so far for the former world No 1, who has not won a match since the Australian Open having lost in the opening round in Doha and last week in Indian Wells.

After that defeat by Naomi Osaka, she parted ways with coach Sven Groeneveld, who had stuck with her through her 15-month doping ban, while she pulled out of last month's tournament in Dubai, also with a forearm problem.

It will be a meeting of the only two former champions in the women's draw, with Sharapova lifting the trophy a decade ago while Kerber was the winner in 2016.

The German endured a miserable 2017, slipping from world No 1 to outside the top 20, but she has been revitalised at the start of this season and is yet to lose a match.

Sharapova, still unseeded after returning from her 15-month doping ban, sees matches against the leading players as the best way to test her level.

Tournament director Craig Tiley has been forced to defend the Open's stance of choosing the 2008 Australian Open champion to conduct the draw less than two years since she tested positive to banned substance meldonium.

Sharapova served a 15-month doping ban for that positive test after she took the controversial medication during the 2016 Australian Open.

The Russian is enjoying her most successful tournament since she returned in April from a 15-month ban for taking the banned substance meldonium.

It was the five-time Grand Slam winner's first appearance since she was beaten by Latvian 16th seed in New York in early September and gets her stop-start return from a 15-month doping ban back on track.

Sharapova, ranked No 104 in the world, is a wildcard in Beijing and she produced a battling performance in Saturday's lively 7-6 (7-3), 5-7, 7-6 (9-7) triumph that lasted over three hours.

The five-time Grand Slam champion returns to the WTA Tour later this month, following a 15-month suspension, after testing positive for the substance at the 2016 Australian Open.

The Russian, who turns 30 next week, had been using meldonium for more than a decade but the substance was reclassified as a banned drug ahead of the 2016 season.

Sharapova, who was originally suspended for two years before having the sentence reduced to 15 months on appeal, makes her competitive comeback in Stuttgart in just over a week.

Florida-based Sharapova was originally banned for two years after testing positive for meldonium at last year's Australian Open.

It says that the UN is looking forward to working with her to discuss her role "at an appropriate date".

The player admitted in March that she had taken the substance meldonium at the Australian Open in January.

She was subsequently banned for two years by an investigating tribunal.

But last month her suspension was reduced to 15 months after she filed an appeal.

Sharapova was given the backdated suspension after she admitted to using meldonium after it was placed on WADA’s list of prohibited substances on January 1.

As with all doping cases, WADA has the right to appeal sanctions given to athletes to the Court of Arbitration for Sport (CAS) if they feel the suspension is too lenient or too harsh.

The body has, however, decided not to exercise that option in the case of Sharapova, who announced yesterday she would be appealing the verdict of the Independent Tribunal to the CAS.