Having already had three operations on her right knee, Li Na knew her career was in jeopardy in March when the left began to swell, too.

“This is a new injury for me,” Li said from Beijing in a phone interview Sunday. “Now the tennis, especially on the women’s side, is really strong. If you want to keep on a high level, you have to keep the body fit. And now I cannot do that anymore, and so I say maybe now is the time because it’s a waste of time if you cannot train 100 percent but still play. This is not myself.”

After playing through pain for months, Li had surgery in late July. When it was clear that a full recovery at 32 would be a much tougher proposition than it was after previous operations, she decided to hang up her racket for good.

Li, who posted a letter on social media Friday revealing that she was retiring, faced reporters for the first time since the announcement at a news conference Sunday in Beijing. As she gave a brief opening statement, tears streamed down her cheeks. But as she took questions, she regained her composure and expressed pride in what she had achieved.