Serena Williams has worried her supporters after abruptly saying 'I'm done' in her post-match press conference following defeat by Naomi Osaka in the semi-finals of the Australian Open. 

The 39-year-old, who is still one behind Margaret Court's all-time record of 24 Grand Slam singles titles, broke down in tears following the straight-sets defeat on Thursday. 

After admitting she 'wouldn't tell anyone' if she did say farewell to the Melbourne crowd upon leaving Rod Laver Arena, the American was visibly emotional and left the press room in tears, saying: 'I can't... I'm done.' 

As the video circulated on social media after her defeat to Japanese star Osaka, some fans were concerned that Williams' retirement could be imminent - while others believe now is the time to call it a day. 

A user summed up the emotions of all, saying: 'Serena has had an amazing career. If she keeps playing, great. If she retires, great.

'She's the goat. She has an amazing family. Her legacy will not be tarnished by a SEMI FINAL loss at 39. If anything, it cements it.'

One user admitted: 'If Serena retires without getting 24, I feel like that's going to sit with her forever' and another added: 'I'm really worried Serena will retire soon.' 

However, others online believe it is now time for Williams to hang up her racket after a career spanning over 25 years. 

'Serena needs to retire to be honest,' a user wrote. 'Watching her face Naomi was sad, she's nowhere near at the moment' and one user thought similarly: 'I honestly don't think Serena can move past semifinals again. If I were her, I'd retire peacefully.' 

Another Twitter user stated: 'Serena needs to retire gracefully. They've been slapping her up and down for the last 4 years. I don't think she's ever making it to #24' 

Williams has now not won a Grand Slam since her triumph in Melbourne in 2017 - and has been chasing Court's all-time major record ever since. 

She has since reached four Grand Slam finals but is yet to get over the line, with one of those coming against Osaka in the 2018 US Open - a match famous for her confrontation with chair umpire Carlos Ramos.  

Williams also lost in the final at Wimbledon in both 2018 and 2019, to Angelique Kerber and Simona Halep respectively, while Bianca Andreescu was also victorious against her in the final at the 2019 US Open. 

Serena later posted an Instagram, saying: 'Melbourne and my Australian fans - today was not ideal outcome or performance but it happens... 

'I am so honoured to be able to play in front of you all. Your support, your cheers, I only wish I could have done better for you today. I am forever in debt and grateful to each and everyone single one of you. 

'I love you. I love you. I love you. I adore you.' 

At a press conference which lasted just over three minutes before she left the room, Williams admitted that she simply made too many errors on court on Thursday. 

'Just made too many mistakes there, easy mistakes,' she said. 

'Not like I was on the run or anything, they were just easy, easy mistakes.

'The difference today was errors. I made so many errors today. Honestly, there were opportunities where I could have won. I could have been up 5-0.'