Peng Shuai, one of China’s most accomplished tennis stars, disappeared from public view in early November after a rare public allegation of sexual assault against a retired top official in China’s Communist Party. The international tennis community, including many of the sport’s best-known global stars and its governing bodies, have openly questioned Chinese authorities on her whereabouts and her allegation.

Who is Peng Shuai?

Peng Shuai (pronounced “Pung Shwai”), 35 years old, is the only Chinese tennis player to ever have...

Peng Shuai, one of China’s most accomplished tennis stars, disappeared from public view in early November after a rare public allegation of sexual assault against a retired top official in China’s Communist Party. The international tennis community, including many of the sport’s best-known global stars and its governing bodies, have openly questioned Chinese authorities on her whereabouts and her allegation.

Who is Peng Shuai?

Peng Shuai (pronounced “Pung Shwai”), 35 years old, is the only Chinese tennis player to ever have attained a world No. 1 tennis ranking—in Ms. Peng’s case, in women’s doubles, in 2014. She won women’s doubles titles in two Grand Slam tournaments, at Wimbledon in 2013 and at the French Open in 2014, winning both times with Taiwan’s Hsieh Su-wei. Ms. Peng represented China at three Summer Olympics, including the 2008 Beijing Games.

Ms. Peng began playing tennis with her uncle at the age of eight and grew up within China’s state-backed system, in which the state provides everything, including housing, training and medical care. In the 2000s, Ms. Peng was among the first Chinese tennis players to break free of the system and hire foreign coaches on her own, though she later returned to the system after a series of reforms. Because the state had invested in her career, Ms. Peng was required to contribute an unspecified portion of her prize winnings to the state.

How long has Peng Shuai been missing?

On the evening of Nov. 2, a post on Peng Shuai’s verified social-media account made a sexual-assault allegation against former Chinese Vice Premier Zhang Gaoli. The post, on China’s Twitter -like Weibo platform, said that Ms. Peng had an on-and-off relationship with Mr. Zhang lasting for some years that was sometimes consensual and sometimes involved coercion, including forced sex. It disappeared after about 20 minutes and she hasn’t been seen in public since. Although Ms. Peng’s social-media account remains online, its comments function has been disabled and her name blocked in searches.

A post on Peng Shuai’s verified social-media account said that she had an on-and-off relationship with former Chinese Vice Premier Zhang Gaoli lasting for some years that was sometimes consensual and sometimes involved coercion.

Photo: Wang Ye/Zuma Press

Nearly two weeks later, on Nov. 14, Steve Simon, chairman of the Women’s Tennis Association, said the organization hadn’t been able to reach Ms. Peng after repeated attempts, and called for an investigation into her allegation.

On Nov. 17, China’s state-run broadcaster published what it said was an email sent by Ms. Peng to the WTA. The screenshotted message said that the sexual-assault allegation is untrue and that “everything is fine.” Mr. Simon subsequently said the email raised more concerns about her safety and whereabouts.

How has the international community responded to Peng Shuai’s case?

The WTA’s Nov. 14 call for China to investigate Ms. Peng’s allegation was quickly echoed by the Association of Tennis Professionals, the world governing body for men’s tennis.

Many of tennis’s most storied figures, including Billie Jean King and Martina Navratilova, as well as current players such as Naomi Osaka, have spoken out in support of Ms. Peng and the WTA’s call for an investigation. “We must not stay silent,” Serena Williams told her over 10 million followers on Twitter.

Beyond the world of tennis, a number of athletes—including Spanish soccer star Gerard Piqué, with his more than 20 million Twitter followers—have tweeted out the hashtag #WhereIsPengShuai.

The International Olympic Committee, which is set to oversee the Winter Olympics in Beijing in February, declined to comment publicly, saying it believed in what it called “quiet diplomacy.”

Peng Shuai is the only Chinese tennis player to ever have attained a world No. 1 tennis ranking—in Ms. Peng’s case, in women’s doubles, in 2014.

Photo: Bai Xue/Xinhua/ZUMA PRESS

How has Beijing responded so far?

Within the country, the sexual-assault allegation has been largely ignored or played down. Foreign Ministry spokespeople have repeated on several occasions that they are unaware of it, though questions and answers about Ms. Peng have been omitted from official transcripts published by the ministry. On China’s tightly regulated internet, some discussion of Ms. Peng’s situation has disappeared. The email attributed to Ms. Peng was published only on the state broadcaster’s international arm, suggesting that it was intended for an audience outside China.

What does this say about China’s #MeToo movement?

The sexual-assault allegation is the first to be publicly leveled at a senior member of China’s ruling party. In recent years, other allegations of sexual misconduct have been made toward figures in Chinese academic and entertainment spheres. In many cases, those making the accusations have ended up being the targets of threats and defamation cases by the men they accused. Women in other countries have also faced defamation lawsuits after making accusations.

The Communist Party itself has acknowledged sex scandals involving its top officials, though typically only after they have been found guilty on corruption or other charges.

Write to Wenxin Fan at Wenxin.Fan@wsj.com