Women's Tennis Association chairman Steve Simon has branded a video appearing to show missing Chinese player Peng Shuai in a restaurant as "insufficient".
Peng, the former Wimbledon doubles champion, is seen smiling in the apparently new footage released by Chinese state media.
Concern for the welfare of the 35-year-old, who has not been heard from directly for more than a fortnight, this week even reached the United Nations and the White House.
The former world No.1 in doubles seemingly disappeared after making allegations of sexual assault against a former vice-premier in China on the social media site Weibo.
Roger Federer, Wimbledon organisers and the Athletes Commission of the International Olympic Committee (IOC) became the latest to voice their concerns for Peng.
Mr Simon has threatened to pull the WTA out of the lucrative Chinese part of its tour next season unless it is proved that Peng is safe, and he reiterated that its relationship with China is "at a crossroads".
"I am glad to see the videos released by China state-run media that appear to show Peng Shuai at a restaurant in Beijing," said Mr Simon in a WTA statement.
"While it is positive to see her, it remains unclear if she is free and able to make decisions and take actions on her own, without coercion or external interference. This video alone is insufficient.
"As I have stated from the beginning, I remain concerned about Peng Shuai's health and safety and that the allegation of sexual assault is being censored and swept under the rug.
"I have been clear about what needs to happen and our relationship with China is at a crossroads."
The video was posted on Twitter by Hu Xijin, editor-in-chief of Global Times, who said it was taken on Saturday and shows Peng with her coach and friends in a restaurant in Beijing.
Earlier on Saturday, Hu Xijin had said that Peng was safe and well in her own home.
Three purportedly new pictures of Peng were also reportedly posted on Chinese messaging app WeChat, along with a "Happy Weekend" message.
Federer said in a statement: "She's one of our tennis champions, a former world No. 1, and clearly it's concerning. I hope she's safe. The tennis family sticks together and I've always told my children as well that the tennis family is my second family. I've been on tour for 20-25 years and I love the tour, I love the people that are there, (they) are special, the players as well, and she's one of them."
A Wimbledon statement said: "We are united with the rest of tennis in the need to understand that Peng Shuai is safe. We have been working in support of the WTA's efforts to establish her safety through our relationships behind the scenes.
"Along with the global tennis community, we would like Peng Shuai to know that her wellbeing is of the utmost importance to us, and we will continue to work to gain clarity on her safety."
The IOC athletes commission said: "Together with the worldwide athlete community, the IOC Athletes Commission is very concerned about the situation of three-time Olympian Peng."
