It came after a spokesperson for the International Tennis Integrity Agency (ITIA) said the 23-time grand slam champion had registered, the first step required by a player seeking to come out of retirement.
The 44-year-old Williams has not competed since bidding farewell at the 2022 US Open. At the time, Williams said she didn't want to use the word "retiring" and instead declared that she was "evolving" away from tennis.
It is not clear when or where - or even if - Williams actually will play again, and she later posted: "Omg yall I'm NOT coming back. This wildfire is crazy."
Her agent did not immediately return a request for comment.
In a statement, US Tennis Association spokesman Brendan McIntyre said: "We are aware that Serena has filed the necessary paperwork with the International Tennis Integrity Agency to reenter the International Registered Testing Pool. If Serena decides to return and compete at the professional level, together with her fans, we will enthusiastically welcome the return of one of the greatest champions in the history of our sport."
Her decision to place her name back in the testing pool with the ITIA, who oversee anti-doping and anti-corruption efforts, was first reported by online Bounces.
"She is on the list and back in the testing pool," ITIA spokesman Adrian Bassett confirmed on Tuesday.
Athletes returning to testing need to provide information on their whereabouts - details on their location when they are not at an official event and times when they are available to give samples.
Someone who retires while they are on the list and later comes back needs to be available for testing for six months before they are allowed to return to competition.
Williams' older sister, Venus, returned to competition last July at 45, after nearly 18 months away from the tour; she never had announced her retirement. At the US Open, Venus became the oldest player to play singles at the American Grand Slam tournament since 1981.
When Venus, a seven-time major singles champion, came back at the DC Open, she spoke about wishing Serena would join her back on tour. They claimed 14 Grand Slam doubles titles as a pair.
"I keep saying to my team: The only thing that would make this better is if she was here. Like, we always did everything together, so of course I miss her," Venus said at the time when asked about a video on social media that showed Serena swinging a racquet. "But if she comes back, I'm sure she'll let y'all know."
