The 44-year-old raised eyebrows late last year after rejoining the tennis anti-doping testing pool, though she denied at the time the move signalled she was preparing to return to the sport she dominated for nearly two decades.
She reignited speculation last month when she deflected questions about a possible return during an appearance on NBC's "Today" show.
The Women's Tennis Association did not immediately respond to a request for comment outside normal business hours.
Williams, who won her last Grand Slam singles title in 2017, has not competed since the 2022 US Open.