"Body in bad shape"

The former world No. 1 had been struggling with multiple injuries a year ago, said Eisenbud. "Her body was in bad shape. The first six months, her body needed rest."

Sharapova overcame a potentially career-ending injury in 2008, undergoing surgery for a torn rotator cuff in her shoulder which kept her off the tour for nine months.

But now, Eisenbud added, Sharapova is fully healthy. The way he put it, the extended break has given her a "third career."

"Before her shoulder surgery, after shoulder surgery and now this.

"I watched her practice last week and I was like, it's a joke just how motivated and how good she was."

With no ranking due to her inactivity, Sharapova needs wildcards to play at top-level professional events and besides Stuttgart, she has already benefited from them for tournaments in Rome and Madrid in May in the buildup to the French Open.

The interest has been there, claimed Eisenbud.

"Every WTA tournament called me, every single one," he said.

Sharapova, though, must wait to find out if she will gain wildcards for Roland Garros and Wimbledon. The new head of the French tennis federation, Bernard Giudicelli, hinted this month that the French Open -- the site of Sharapova's last two major titles in 2012 and 2014 -- may bypass the US-based athlete.

Sharapova, who turns 30 the week before her comeback, last played a professional tennis match at the Australian Open in January 2016, when she lost in the quarterfinals to eventual champion Serena Williams. Her subsequent ban meant Sharapova couldn't play at the last Olympics in Rio in August.

Long breaks

With a 10-month season for the women and 11 months for the men, tennis has one of the longest and most grueling schedules in professional sports and players in their 30s are now proving time off can be beneficial.

At this year's Australian Open, Roger Federer returned from a six-month break -- he was recovering from a knee injury -- and won his first major title since 2012.

As he gets older, the 35-year-old Swiss has started to schedule his year in four mini-seasons which consist of tournaments followed by lengthy breaks to rest and recover.

Earlier in his career, he also took breaks.

"I always felt like breaks were important for me," Federer said in Melbourne. "I remember some years I wouldn't hit tennis balls for four to five weeks. I think that was really important for me to look at the longevity aspect."

Women's world No. 1 and 23-time major singles champion Williams -- also 35 -- has likewise benefited from taking time off, particularly at the end of the season, to let her body recover.

Harvard Business School

Although Sharapova was initially given a two-year ban by the International Tennis Federation, her suspension was cut to 15 months on appeal by the Court of Arbitration for Sport in October. The Swiss-based court said "under no circumstances...can the player be considered to be an 'intentional doper.'"

Sharapova, who became a global star and the world's highest-paid female athlete for a decade after she won Wimbledon in 2004 at the age of 17, has kept herself busy during her break from tennis.

She has been working on her memoirs and promoting her wholly-owned candy brand, Sugarpova, which last year made its first foray into chocolate.

Sharapova also attended classes at Harvard Business School during the North American summer and did internships at the NBA, a London-based advertising agency and Nike, one of her longtime sponsors.