Serena Williams voiced concern for fellow tennis player Peng Shuai, who has not been seen publicly since she accused a former vice-premier of China, Zhang Gaoli, of sexual assault.
In her now-deleted post on China's Twitter-like Weibo, Peng had written "why did you take me to your house and force me into having relations with you?", though she also described the relationship with Zhang as an on-off one that was also consensual.
Peng could be seen in the stands wearing a black knit hat with the Olympic rings on them and a black coat with the Chinese flag.
Djokovic says Peng situation horrifying, says tennis must unite.
Yao said he and Peng had known each other for nearly 20 years. However, he did not comment directly on the controversy that flared up last year after Peng, a former world No. 1 doubles player, appeared to allege that a former vice premier, Zhang Gaoli, had sexually assaulted her in the past.
Peng's presence during the Games had been a matter of speculation since the IOC said it planned to meet with her in Beijing.
Tennis great and founder of the WTA Billie Jean King was among those who applauded the announcement.
Chinese tennis star Peng Shuai said on Sunday that she had never accused anyone of sexually assaulting her, and that a social media post she had made early last month had been misunderstood.
Chinese tennis star Peng Shuai, whose whereabouts have been a matter of international concern for weeks, attended a tennis tournament in Beijing on Sunday.
An outcry over the whereabouts of Chinese tennis star Peng Shuai escalated on Friday as the Women's Tennis Association (WTA) said it was prepared to pull its tournaments out of China if they were not satisfied with the response to her sexual assault allegation.
The United States and Britain had also called for China to provide proof of Peng's whereabouts.
Most of the companies are Chinese and surprisingly all are diversified banks.
The Chinese Communist Party's all important 19th Party Congress is just months away, and President Xi Jinping finds himself confronting unlikely challenges to his pre-eminent position, says former RA&W officer and China watcher Jayadeva Ranade.
The chaos on its stock markets, a fierce battle between the old and new guard in the Communist Party and the restive border provinces of Tibet and Xinjiang forebode tough times ahead for China, says Claude Arpi.
What was the need for Xi Jinping, general secretary of the Chinese Communist Party, President of the People's Republic of China and Chairman, Central Military Commission, to don the new role of Commander in-Chief? Does this mean that the most powerful Chinese leader since Mao faces numerous threats from within the Communist Party?