PARIS - Novak Djokovic hailed Maria Sharapova as a "legend" with "the mind of a champion" after the Russian superstar announced her retirement from tennis at the age of 32 on Wednesday.

Five-time Grand Slam champion and former world No 1 Sharapova called time on her career after losing a long-term battle with shoulder trouble having amassed a total of 36 WTA titles, spending 21 weeks at the top of the rankings and with a personal fortune estimated at $300 million.

"Her impact on the sport, not just women's tennis, but tennis in general, was great. It still is great," said world No 1 Djokovic in Dubai where he made the quarterfinals on Wednesday.

"She's a very smart girl, someone that I know very well for a long time. She has the mind of a champion, someone that never gives up. She's shown that especially in the last five years.

"She had a lot of obstacles and difficulties, especially with her injuries and everything that she had to endure in order to give herself at least another chance to play competitive tennis.

"For someone that has won five Grand Slams and has been number one of the world, a legend of the sport, she should be proud of everything she has achieved."

US legend Billie Jean King said Sharapova had been a "great champion" ever since becoming an overnight sensation as a 17-year-old Wimbledon champion in 2004.

"From the day @MariaSharapova won her first #Wimbledon title at age 17, she has been a great champion. A 5x major champion and a former World No 1, her business success is just as impressive as her tennis achievements. Maria, the best is yet to come for you! #MissYouMaria," tweeted 12-time major winner King.

Petra Kvitova, a two-time Wimbledon winner, who defeated Sharapova in the 2011 final at the All England Club, praised the Russian's "hard work and fight".