World No. 1 Serena Williams will not play any more tournaments this season, according to a story posted on the China Open website. Williams was scheduled to play next week in Beijing and also qualified for the WTA Finals in Singapore.

The 34-year-old said she has been hurt much of the year and was clearly upset after losing in the semifinals of the U.S. Open to Roberta Vinci. Had Williams won the U.S. Open, she would have completed a calendar-year Grand Slam.

The 34-year-old finishes her year 53-3, with five titles (Australian Open, Miami, French Open, Wimbledon, Cincinnati). She also withdrew from three tournaments (Indian Wells, Rome, Bastad). Her losses were to Petra Kvitova, in Madrid, to Belinda Bencic, in Toronto, and to Vinci in New York.

“It’s no secret I’ve played injured most of the year—whether it was my elbow, my knee, or, in the finals moments after a certain match in Flushing, my heart,” Serena was quoted as saying. “I’m a fierce competitor. And I want to compete as well as I can, for as long as I can. So I am taking a proactive step and withdrawing from tournaments in Beijing and Singapore to properly address my health and take the time to heal.”

The 21-time Grand Slam singles champion had said that pressure on her was building before the U.S. Open began, and she knew says that her body was in pain. But she added that she will return to the tour in 2016 and will play some year-end exhibitions.

“This is a very difficult decision, but one ultimately made because of the love of the game. I plan to return to practicing and participating in exhibition matches later this year,” Williams said. “And when I do, I will focus and focus and focus so I can continue my journey in this beautiful game.”

Late-season withdrawals are not uncommon for Williams. After losing the 2011 U.S. Open final to Samantha Stosur, Williams didn't play the rest of the year. In 2012, she won the U.S. Open and didn't play again until the season-ending championships in Istanbul, which she won. In 2013, Williams defended her U.S. Open title and played just one tournament in Asia, Beijing, which she won. She then went to Europe, where she won the WTA Final in Istanbul.

Last season, Williams won the U.S. Open for the third time in a row, then retired from her opening-round match in Wuhan and withdrew before her quarterfinal in Beijing. She ended up winning the WTA Final in Singapore.