Naomi Osaka has not played a tennis match since September and her withdrawal from next week's Australian Open has raised concerns that the former world number one may never appear on court again.
Osaka's social media accounts have stayed silent since Tennis Australia tweeted on Sunday that the two-time Melbourne champion would miss the first Grand Slam of the year, giving no reason for her absence.
Osaka's posts over the past few months have shown her travelling in Europe with her boyfriend, the rapper Cordae, and announcing that her sports management agency had signed up world number two Ons Jabeur.
But there has been little evidence of the Japanese player spending time practising on court, fuelling speculation that the four-time Grand Slam champion's tennis career could be over at the age of 25.
Tennis writer Ben Rothenberg, who has authored a biography of Osaka due out later this year, believes she has already taken a "meaningful step back" from the sport and is deliberately keeping quiet.
"I think she might want to be opaque about it because she doesn't want to put a label on it necessarily," he told AFP.
"I don't think she would use the word 'retiring', but if she was stepping away from the sport for a while -- and it could be for any length of time -- I don't know that she would want to speak that out loud.
"I think she would sense that that would raise a lot of bells and whistles."
- 'More down than up' -
Osaka has previously talked about struggling with her mental health and revealed that she suffered depression.
She spent all of 2022 outside the top 10, enduring first-round defeats at both the French and US Opens and withdrawing from Wimbledon with an Achilles' injury.
She also split from long-time coach Wim Fissette last summer, replacing him with her father Leonard Francois.
Her last appearance was at the Pan Pacific Open in Tokyo in September, where the home favourite withdrew before her second-round match, complaining of abdominal pain.
She told reporters at that tournament that she had gone through "more down than up" in 2022 and that she had "learned a lot" about herself.
She is now ranked 47 in the world, having hit the summit for the first time in 2019.
Rothenberg believes Osaka is "recalculating things" and may decide that she is not prepared to make the sacrifices needed to continue as a professional tennis player.
"For her, the math is not adding up right now, for her to want to make the commitment," he said.
"She knows how much work it is and how all-encompassing and preoccupying it is to be an active full-time player with the standards that she has.
"She's won so much already, she's not going to be content just to be a top-20 player again."
Australia's Ashleigh Barty, then the world's undisputed number one, stunned the tennis world in March last year when she announced her retirement aged 25.
She explained that she was "spent physically" and no longer had the drive needed to continue.
- Business interests -
Osaka has several interests outside of playing tennis, including her sports management agency Evolve, which counts Jabeur and Australian tennis star Nick Kyrgios among its clients.
She has also invested in Pickleball, a tennis-like sport that is growing fast in the United States, and boasts numerous endorsements.
Her website describes herself as not only a tennis player but also "fashion nerd", "entrepreneur" and "social change advocate".
Osaka was named the world's top-earning woman athlete for 2022 by Forbes, with reported earnings of $51.1 million, even as her tennis career continued to dive.
Rothenberg says there will be significant pressure from sponsors urging Osaka to "stay on the hamster wheel" of professional tennis.
But he says the fact that she has chosen not to proves that she is "making this decision for herself".
"Whatever her reasons may be, players almost always err on the side of choosing to play," he said.
"So for her to hit pause, I think shows a good deal of control of the situation."
And Rothenberg believes there is still plenty of time for Osaka to come back, should she wish to.
"She has more runway in front of her if she wants to take back off again and get back on tour," he said.
"But it won't get any easier with more time off. The more time she spends away, it will not get easier."