BEIJING - 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.

Following is her farewell and retirement letter:

Special: Li Na retires from tennis

For close to fifteen years, we've been a part of each other's lives. As a tennis player representing China on the global stage, I've trekked around the world playing hundreds of matches on the WTA tour, for China's Fed Cup team, at the National Games and at several Olympic Games. You've always been there for me, supporting me, cheering me on, and encouraging me to reach my potential.

Representing China on the tennis court was an extraordinary privilege and a true honour. Having the unique opportunity to effectively bring more attention to the sport of tennis in China and all over Asia is something I will cherish forever. But in sport, just like in life, all great things must come to an end.

2014 has become one of the most significant years in my career and my life. 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. It was also a year filled with difficult moments, such as having to deal with the inevitable - making the decision to end my professional tennis career.

The amazing moment in Australia was filled with joy, happiness and extraordinary sense of accomplishment. 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. 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.

Most people in the tennis world know that my career has been marked by my troubled right knee. The black brace I wear over it 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.

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. My previous three surgeries were on my right knee. My most recent knee surgery took place this July and was on my left knee. After a few weeks of post-surgery recovery, I tried to go through all the necessary steps to get back on the court. While I've come back from surgery in the past, this time it felt different. One of my goals was to recover as fast as I could in order to be ready for the first WTA tournament in my hometown of Wuhan. As hard as I tried to get back to being 100%, my body kept telling me that, at 32, I will not be able to compete at the top level ever again. The sport is just too competitive, too good, to not be 100%.

Winning a Grand Slam title this year and achieving a ranking of World No.2 is the way I would like to leave competitive tennis. As hard as it's been to come to this decision, I am at peace with it. 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.

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.

In 2010, there were two professional women's tennis tournaments in China. Today, there are 10, one of them in Wuhan, my hometown. That to me is extraordinary! Serena Williams, Maria Sharapova and Venus Williams - with thirty Grand Slam singles titles among them - are coming to my hometown to play tennis for the fans of China! Just as I didn't think I could ever be a Grand Slam champion, never in my wildest dreams did I imagine that some of the best female athletes in the world could play tennis in Wuhan, in my backyard.

My contributions to the growth of the sport in China are very special to me. But I don't want to stop here. Together with IMG, my management company, we are putting together various plans on how we will continue to grow the sport of tennis in China. These plans include opening the Li Na Tennis Academy, which will provide scholarships for the future generation of Chinese tennis stars. I will also stay involved in the Right to Play, an organization dedicated to helping underprivileged children overcome challenges through sport. My philanthropic work will expand in scope as I continue to dedicate myself to helping those in need. What was once just a dream in China today is a reality.

On a personal side, I look forward to starting a new chapter of my life, hopefully having a family and reconnecting with those I did not have the luxury of spending a lot of time with while playing. I can't wait to revisit all the amazing places I played tennis in and see the world through a new set of eyes. I look forward to slowing down and living my life at a new, slower, relaxed pace.

Tennis is an individual sport and as players, our job is to spend a lot of time focusing on ourselves. But no player can ever become a champion alone and nobody knows this better than me. There isn't enough space here to thank everyone who has travelled on my journey with me and contributed to my success. But I must thank those that have stuck with me through the highs and the lows and have helped me become the person that I am today.