Where is Peng Shuai? World's top tennis players v China's Communist Party

China's Peng Shuai serves to France's Caroline Garcia during their French Open second-round match at Roland Garros in May, 2018. Photo / AP

Some of the world's most famous tennis players, distraught by the disappearance of colleague Peng Shuai, are challenging China's Communist Party to get answers.

So far it's a standoff with little visible impact as tennis players like Naomi Osaka, Serena Williams and Novak Djokovic — joined by tennis governing bodies, human rights groups, retired players, and several athletes' lobbies— try to turn their profiles into power.

Peng disappeared after making allegations of sexual assault over two weeks ago against former vice-premier Zhang Gaoli who was a member of the all-powerful Politburo Standing Committee and a lieutenant of General Secretary Xi Jinping.

Athletes may sense a pressure point.

China is just 2 1/2 months from hosting the Beijing Winter Olympics, which is facing a diplomatic boycott over allegations of crimes against humanity involving at least 1 million Uyghur Muslims and other ethnic minorities. NBA player Enes Kanter has been the most outspoken in defence of the Uyghurs, calling Xi a "brutal dictator."

Peng's case is unique. She is a star athlete and has a platform and credibility that few other women in China share. The effort to silence Peng reflects the Communist Party's determination to squelch criticism of its leaders and to prevent any organised public response.

Athletes are especially sensitive politically because they are well-known and admired. The ruling party publicises their victories, especially those of a three-time Olympian such as Peng, as evidence it is making China strong again.

China's Foreign Ministry has repeatedly disavowed any knowledge of the case. Ministry spokesman Zhao Lijian told media on Friday the issue is "not a diplomatic question and I'm not aware of the situation".

China's Foreign Ministry is sticking to its line that it isn't aware of the controversy surrounding tennis professional Peng Shuai. Photo / AP

Peng wrote a lengthy social media post on November 2 in which she said she was forced to have sex three years ago with Zhang. The post was quickly deleted from Peng's verified account on Weibo, a leading Chinese social media platform. But screenshots of the explosive accusations were shared on the internet.

Athletes have been weighing in ever since.

"Censorship is never OK at any cost," Osaka wrote on social media, adding the hashtag #WhereIsPengShuai.

Williams added: "This must be investigated, and we must not stay silent."

"This is horrifying. I mean, a person is missing," Djokovic said at the ATP Finals in Turin, Italy. "The whole community, tennis community needs to back her up and her family, make sure that she's safe and sound because if you would have tournaments on Chinese soil without resolving this situation, it would be a little bit strange."

Players have been emboldened by the unequivocal support of the Women's Tennis Association and its chairman and CEO Steve Simon. Simon has threatened to pull the WTA's events out of China. That means almost a dozen next year, including the WTA final.

"There are too many times in our world today when you get into issues like this that we let business, politics, money dictate what's right and what's wrong," Simon said in an interview on CNN.

"And we're definitely willing to pull our business and deal with all the complications that come with it because ... this is bigger than the business."

The Professional Tennis Players Association has called for player solidarity to defend Peng, who is known as a fearless competitor.

China's Foreign Ministry is sticking to its line that it isn't aware of the controversy surrounding tennis professional Peng Shuai. Photo / AP

"We must unite and be willing to take action unless corroborated evidence is provided to the world about Peng Shuai's wellbeing," the association said.

US Deputy Secretary of State Wendy Sherman tweeted: "We are deeply concerned by reports that tennis player Peng Shuai appears to be missing, and we join the calls for the PRC to provide independent, verifiable proof of her whereabouts. Women everywhere deserve to have reports of sexual assault taken seriously and investigated."

Liz Throssell, a spokeswoman for the UN human rights office in Geneva, said on Friday it was calling for "an investigation with full transparency into her allegation of sexual assault."

Global Athlete, an advocacy group, has asked the Switzerland-based International Olympic Committee to suspend the Chinese Olympic Committee until Peng's safety is guaranteed.

"The IOC must use its substantial leverage to ensure that the international community is provided proof of Peng's whereabouts, that Peng is immediately given safe passage out of China, and that a full and transparent investigation is conducted into her allegations of sexual assault," Global Athlete head Rob Koehler said in a statement.

Despite Peng being a former Olympian, the IOC has remained quiet. A sports business, it derives 91 per cent of its income from selling broadcast rights and sponsorships. But it prefers to cast itself as a non-government organisation whose role is to defend high-minded ideas like "promoting a peaceful society concerned with the preservation of human dignity," which appears in its Olympic Charter.

Kirsty Coventry, the head of an IOC's Athletes' Commission that is supposed to represent the interests of Olympic athletes, has not commented. The IOC always says athletes are their first priority, but there is growing pressure from some athletes to get a larger slice of the IOC's billion-dollar pie.

"Experience shows that quiet diplomacy offers the best opportunity to find a solution for questions of such nature." the IOC said in a statement. "This explains why the IOC will not comment any further at this stage."

It also said it has received assurances that Peng is "safe."

"It's astonishing that the IOC would accept the government's assurances, particularly as the expense of a female Olympian making grave allegations," Human Rights Watch said.

The World Olympians Association declined to issue a statement. It claims to represent 100,000 living Olympians. It was founded by Juan Antonio Samaranch Jr, who heads the IOC preparations for the Beijing Olympics which begin Feb. 4. IOC President Thomas Bach is the honorary president.

"The IOC has more leverage than any other organization with the pending Winter Olympic Games," Koehler of Global Athletes wrote to AP. "They need to use that now. Athletes going to these Games are watching how the IOC will protect athletes."