Peng, a former Wimbledon and French Open doubles champion, has not been heard from since alleging two weeks ago that a powerful Chinese politician sexually assaulted her.

“The statement released today by Chinese state media concerning Peng Shuai only raises my concerns as to her safety and whereabouts,” WTA chief Steve Simon wrote in a statement.

“I have a hard time believing that Peng Shuai actually wrote the email we received or believes what is being attributed to her,” he added.

State-run CGTN published an email Wednesday attributed to Peng, which the player allegedly sent to WTA officials.

Peng, 35, alleged on the Twitter-like Weibo earlier this month that former vice-premier Zhang Gaoli had “forced” her into sex during a long-term on-off relationship.

“Peng Shuai displayed incredible courage in describing an allegation of sexual assault against a former top official in the Chinese government,” said Simon.

He called for “independent and verifiable proof that she is safe”.

“I have repeatedly tried to reach her via numerous forms of communication, to no avail,” said Simon, adding that Peng “must be allowed to speak freely, without coercion or intimidation”.

Details of Peng’s reported accusations remain scrubbed from China’s Internet.

The post appeared to have been deleted quickly and AFP was unable to verify the authenticity of the screenshots containing the allegation, or substantiate the claims made in them.

Four-time Grand Slam champion Naomi Osaka said that she was in “shock” about Peng, with Novak Djokovic and numerous other players in recent days saying they were deeply worried about her.

The WTA urged Sunday for Peng’s claims to be “investigated fully, fairly, transparently and without censorship”.

Chinese officials have remained quiet about Peng and its national tennis association did not respond to AFP requests for comment.