(CNN) -- When Maria Sharapova underwent shoulder surgery five years ago, many thought her tennis career wouldn't last. But there is now a good chance the four-time grand slam winner will play into her 30s before fully turning her attention to her numerous business interests.
"I think she's going to play another four to five years and through the Rio Olympics (in 2016) if she stays healthy and hungry," her long-time agent and close friend Max Eisenbud told CNN's Open Court.
Sharapova's motivation has never been an issue in the past, and the Russian -- who turned 26 last week -- is now fully fit.
That, however, wasn't the case in 2008, when the shoulder injury ruled her out for nine months and cast doubt on Sharapova's professional career, which began on the day she turned 14.
She had been experiencing discomfort in her right -- and serving -- shoulder, with initial tests leading doctors to believe inflammation was the cause. When the pain intensified after a win at a tournament in Montreal in July 2008, she underwent an MRI that revealed two small tears in the tendon of her shoulder.
So began the long process of rehabilitation, surgery, another stint of rehab and dealing with another injury, a bone bruise. It was a difficult time for Sharapova.
"The shoulder, it's a huge part of the tennis game," she told Open Court. "The serve is huge and my game is all about being aggressive and powerful strokes, so when you're out of the game nine months, when you don't have too many examples of athletes coming back after such an injury, of course you have doubters."
Sharapova never lost faith that she would recover, but she would have to wait another three years before reaching another grand slam final, losing at Wimbledon in 2011. Thankfully for Sharapova, no such serious injuries have reoccurred, although she was troubled by an ankle problem later that year.
"I had to work through a lot of things, and more mentally as well because I always thought that during those months that I was away, everyone was working and everyone was training and everyone was playing so it kind of felt like I was left behind a little bit," she said.
Eisenbud's pronouncement about Sharapova's future comes as a boost to the women's tennis tour due to Sharapova's enormous star power and fan base, which increased when she won the French Open last June to cap her comeback and become just the 10th woman to capture all four majors.
Sharapova was last year named by Forbes as the world's 71st most powerful celebrity. She was the highest-ranked female athlete on the list, ahead of Serena Williams, despite the American now owning 11 more grand slam titles.
Sharapova is, according to Forbes, the world's highest-paid female athlete, pulling in almost $28 million -- more than her career prize money -- over a 12-month period that ended last July.
Sponsors including Samsung, Evian, Nike, Tiffany & Co., Head, Cole Haan and, most recently, Porsche help pad Sharapova's wallet. The Florida-based Russian has also launched Sugarpova, her own premium candy line, in the U.S. and plans on expanding to China, Japan, India and England.
But Sharapova remains adamant that success on the court is her first priority. The rest will follow.
"Do I want my candy to sell? Do I want my partnership to continue for many years? Of course I do," Sharapova said. "That's a no-brainer. But at the end of the day all the things that have come to me, that I've been able to be a part of, is because I'm a tennis player, not because I'm a model or because of acting. The core of what I have is my tennis."
Her results in 2013 confirm Sharapova's drive. Known as one of tennis' toughest competitors and hardest workers, she has showed no signs of slowing down.
The power baseliner has reached at least the semifinals in all four of her tournaments and almost completed a rare double at the BNP Paribas Open in Indian Wells and Miami's Sony Open. She won the title in California in March but was defeated by Williams in the finale in Florida two weeks later.
Her poor record against Williams might add to her hunger. Williams beat Sharapova for the 11th straight time, although Sharapova won a set off the world No. 1 for the first time in five years.
Sharapova lacks an Olympic gold medal, too, having been crushed by Williams in the gold medal match at London 2012 and missing 2008 in Beijing with the shoulder injury.
"I always feel like I can be better and when I do step on the court, I feel a certain power with what I'm doing," Sharapova said. "I feel strong and I feel like I'm good at what I do.
"I want to keep working, and I want to keep getting better because you can't stand still. Everyone's working. I'm sure everyone's getting stronger and getting faster and hitting the ball harder. You have to do it as well."
Sharapova begins her clay-court swing as defending champion in Stuttgart this week before competing at the Madrid Open and Italian Open in Rome ahead of her title defense at Roland Garros, which starts May 26.
Her titles in Stuttgart and Rome in 2012 served as the springboard to her success in Paris, where Sharapova downed Italian Sara Errani in the final.
Having come back from the abyss that her career-threatening injury presented, Sharapova savored the success -- especially after being written off by many critics while she was rebuilding her career, suffering some morale-sapping defeats.
"Losing is never easy, especially when you've achieved so much great success and having lifted beautiful trophies," she said.
"And especially when you hear it from people that, you know, they sit there and comment on what you're doing and they don't comment on the work that you put in before something like that, before getting to the stage of a match in front of thousands of people.
"But it makes you so much stronger, and I've looked back and, you know, the people I felt had that connection with me, I've certainly spoken with them about it and especially had a few words with them after the French Open.
"But it's sport. It's normal. I think the world revolves around comments and opinions, and I have absolutely nothing against it."