Serena back in the gym, eyes Aust Open

Serena Williams has returned to training in the gym following the birth of her first child, as she prepares to play at the Australian Open in January.

Serena Williams is back in the gym ahead of another trip to the Australian Open next year. (AAP)

Following the birth of her first child in September, US tennis star Serena Williams is back in the gym, with a view to returning to the WTA tour in January and playing at the Australian Open.

"Serena is already training in the gym to regain form slightly," the former world No.1's physical therapist, Ruben Mateu, told dpa.

Williams, 36, has not played competitive tennis since she won her 23rd Grand Slam tournament in January in Australia. On September 1, she gave birth to her daughter Alexis Olympia Ohanian Jr.

Mateu, who has been part of Williams' team for a year, is set to fly to Palm Beach, Florida, in the coming days to contribute to the tennis star's recovery. However, he is not worried about her prospects.

"When someone's muscles are so well-developed, it is easier for them to recover because muscles have a memory. It is easier to achieve results with that kind of person," Mateu explained.

"The capacity for recovery will be faster for Serena than for any other sportswoman at her level."