Britain's Andy Murray says he plans to retire after this year's Wimbledon but fears next week's Australian Open could be the final tournament of his career.
The three-time Grand Slam winner, who is struggling to recover from hip surgery, was in tears at a news conference in Melbourne on Friday.
"I'm not sure I'm able to play through the pain for another four or five month," said the 31-year-old Scot.
"I want to get to Wimbledon and stop but I'm not certain I can do that."
However, Murray says he still intends to play his Australian Open first-round match against Spanish 22nd seed Roberto Bautista Agut next week.
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The former world number one had surgery on his right hip last January and has played 14 matches since returning to the sport last June.
Murray ended his 2018 season in September to spend time working with rehabilitation expert Bill Knowles but still looked short of the required level when he played world number one Novak Djokovic in an open practice match at Melbourne Park on Thursday.
In his news conference - during which he left the room to compose himself before returning - Murray said: "I'm not feeling good, I've been struggling for a long time.
"I've been in a lot of pain for about 20 months now. I've pretty much done everything I could to try and get my hip feeling better and it hasn't helped loads.
"I'm in a better place than I was six months ago but I'm still in a lot of pain. I can still play to a level, but not a level I have played at."
'The pain is too much - I need to think about my quality of life'
Murray was frank in his assessment of his abilities, conceding he is no longer able to perform to the level at which he won the US Open in 2012 and Wimbledon in 2013 and 2016.
He told the world's media of the agonising pain he is in when playing and says further hip surgery might be needed to ensure he has a better quality of life in retirement.
"The pain is too much really," said Murray, who is also a two-time Olympic champion. "I need to have an end point because I'm playing with no idea of when the pain will stop.
"I'd like to play until Wimbledon - that's where I'd like to stop playing - but I'm not certain I'm able to do that."
Speaking to BBC Sport, he added: "A second surgery is an option. I wouldn't be taking the option to have a surgery to resurface and replace my hip with the view to playing at the highest level again. The number one reason to have something so serious is improve your quality of life and being in less pain.
"Athletes have had operations like that done and come back to play - but certainly not in tennis and in singles.
"If I do that I'm not sure I will be competing again."
Murray, who was knighted in the Queen's New Year Honours list at the end of 2016, also ruled out becoming a doubles player in the future, ending the possibility of him teaming up with older brother Jamie in the twilight of his career.
From the moment Andy Murray walked into the news conference at Melbourne Park, you felt a sense that something wasn't quite right.
Asked a simple opening question of how he was feeling, an emotional Murray struggled to get an answer of "not great" out before covering his face with his cap and sobbing underneath.
Murray has often showed his emotion on court but this was different. This was raw emotion in a place where players - and indeed sport stars generally - don't like to show their true feelings in front of the world's media.
A sombre silence filled the room after Murray temporarily left - before he returned, a little more composed, and managed to tell us more.
The toils of the past four months - going to Philadelphia to work with rehab expert Bill Knowles and realising he still can't reach the required physical level which brought him three Grand Slam titles, plus perhaps the harsh reality of being unable to compete with Novak Djokovic in a practice session here on Thursday - have hit Murray.
Despite his fragile state, he still managed to fulfil his media duties and there was even evidence of his dry wit coming out as he was interviewed by television crews after the main news conference.
But a cracking voice was never far away as he discussed the pain in his hip and in his mind as he contemplated his future.
And when his media duties were done, the tears flowed again between him and coach Jamie Delgado as they shared an embrace in a media centre corridor.
Murray's career in numbers
3 Grand Slams 37 weeks as world number one
2 Olympic gold medals 14 Masters 1000 titles
1 ATP Finals 8 Grand Slam finals