BEIJING, Sept. 19 -- China's first and only Grand Slam winner Li Na formally announced her retirement on Friday, leaving the Chinese tennis yearning for the next superstar.

Li, 32, made the announcement on her microblog, the Chinese equivalent to Twitter, a day after rumors about her leaving aleady spreaded all over the internet and social media.

Li called 2014 "one of the most significant years" in her career and her life, but it was also a year "filled with difficult moments".

"This year was full of amazing highlights, which included winning my second Grand Slam singles title at the Australian Open and sharing the extraordinary experience with my country, my team, my husband and my fans." Li wrote in a farewell letter on her microblog.

Experiencing ups and downs in 2012 and 2013 following her 2011 French Open triumph, Li found the top of her game again this year, bagging a second Grand Slam title in the Australian Open.

"The task of finally making a decision to hang up my racquet felt a lot more difficult than winning seven matches in a row in the Australian heat," said the Wuhan native who quit tennis on the opening day of the WTA event in her hometown Wuhan, capital city of Hubei Province.

Li's retirement came as a surprise but an understandable decision. Speculation has been rife since she pulled out of the U.S. Open and other hard-court tournaments because of knee injuries that flared up in July.

The tenacious player eventually surrendered to recurrent knee injuries that had bothered her entire career.

"The black brace I wear over it (the right knee) when I step on the court has become my tennis birth mark. And while the brace completes my tennis look, the knee problems have at times overtaken my life.

"It took me several agonizing months to finally come to the decision that my chronic injuries will never again let me be the tennis player that I can be. Walking away from the sport, effective immediately, is the right decision for me and my family," she said.

"After four knee surgeries and hundreds of shots injected into my knee weekly to alleviate swelling and pain, my body is begging me to stop the pounding," she added.

Her husband Jiang Shan revealed that Li is currently receiving treatment on both her knees in Germany and expected to fly back to Beijing to attend a news conference on Sunday.

Looking back at her playing career, Li could leave without regrets.

"I have no regrets. I wasn't supposed to be here in the first place, remember? Not many people believed in my talent and my abilities, yet I found a way to persevere, to prove them (and sometimes myself!) wrong," she said.

Starting up as a badminton amateur at five, Li turned to tennis and joined the ITF tour in 1996, the year her father passed away.

Li soon made her name as a promising star in the country, winning the national youth title a year later before she began to play in the WTA tour in 2000 but suddenly dropped the sport to become a journalism student in Huazhong University of Science and Technology.

In 2004, she came back from two years of retirement and lifted her first ever WTA title in Guangzhou.

Since then, she had been on the track of recording breaking, fighting into Wimbledon last eight in 2006 to become the first Chinese ever going this far at any Grand Slam event.

The real breakthrough came in 2011 when she won the first Grand Slam title at French Open for Asia.

"I've succeeded on the global stage in a sport that a few years ago was in its infancy in China. What I've accomplished for myself is beyond my wildest dreams. What I accomplished for my country is one of my most proud achievements." she concluded.

With her achievements and controversial personality, Li sure will be missed as a unique and accomplished tennis great in China.

The WTA Tour dedicated headline stories to Li, who gave a huge push of the sport in the country of 1.3 billion people.

"Li Na has been a fun, powerful, and wonderful player on the WTA tour and, along with her fans, I am sad to hear that she has retired. In addition to her amazing tennis abilities and her warm and humorous personality, she is a pioneer who opened doors to tennis for hundreds of millions of people throughout China and Asia," WTA Chairman Stacey Allaster said about the cover girl for last year's Time magazine issue which listed her among the world's 100 most influential people.

The Chinese tennis association thanked Li for her contribution and gave her the best wishes although the two parties were not always on good terms.

Li once criticized the association for "unfair distribution of competition bonus" and refused at times to be labled "playing for the country".

Under Li's microblog were left over 70,000 comments and 150,000 forwards just five hours after her announcement.

"I am sad just to think about you leaving the court," said one net user Stupidboy.

"Goodbye, Na. You will always be the pride of China,"said Wryuan_chan.

As Li waved farewell to professional tennis, China lost another high profile figure that enjoyed international fame. Former NBA center Yao Ming put an end to his playing days in 2011.

As far as tennis concerned, one may wonder when the next "Li Na" will show up or ever will.

Peng Shuai, four years younger than Li, reached her career peak this summer -- the semifinals of the recent U.S. Open -- and raised Chinese' fans expectations on her.

Veteran Zheng Jie, 31, focuses more on doubles than singles while third highest ranked Zhang Shuai, world number 33, has yet to overcome the first round at any Grand Slams.

Also playing in the WTA tour are Zheng Saisai, 20, and Wang Qiang, 22, who both linger outside the top 100 in the world rankings.

"We surely don't like to see a big gap between Li Na and her successors. Even though there is no player as outstanding as she is, we are perfectly happy if we can have 10 players stay in the top 100 in the future," said Chinese women's tennis coach Wang Peng.