Former world No.1 Andy Murray, who has not played since July because of injury, has withdrawn from this week's Brisbane International due to long-term issues with his right hip and has said he may need surgery.
With the Australian Open starting on January 15, the Briton's withdrawal from Brisbane raises doubts about the 30-year-old's participation in the first major of the year, a tournament he has finished runner-up on five occasions.
In a lengthy post on his Instagram page, Murray said he will stay in Australia over the next few days and decide over the weekend whether to remain Down Under or return to Britain.
"In the short term I'm going to be staying in Australia for the next couple of days to see if my hip settles down a bit and will decide by the weekend whether to stay out here or fly home to assess what I do next," he said.
Novak Djokovic, winner of 12 grand slams, was also an absentee from the second half of the tour last year and has also delayed his comeback, saying last week that he had "started to feel pain" in his right elbow.
Meanwhile, world No.1 Rafael Nadal has announced he will make his return to the sport, after withdrawing from November's World Tour Finals with a knee injury, at an exhibition event in Melbourne next week.
The Spaniard withdrew from the Brisbane International last week, saying he was "still not ready after last year's long season," but said he intended on playing at the Australian Open.
Stan Wawrinka (knee), Milos Raonic (wrist), Kei Nishikori (wrist) are other major names who are bidding to overcome injury concerns before the Australian Open begins.
'Difficult period' for Murray
Murray, now ranked 16th in the world, attempted a return at the US Open in August but pulled out two days before the start of the tournament and his only on-court appearances since have been exhibitions.
"I've obviously been going through a really difficult period with my hip for a long time and have sought council from a number of hip specialists," he added on Instagram.
"Having been recommended to treat my hip conservatively since the US Open I have done everything asked of me from a rehab perspective and worked extremely hard to try get back on the court competing.
"Having played practice sets here in Brisbane with some top players unfortunately this hasn't worked yet to get me to the level I would like so I have to reassess my options. Obviously continuing rehab is one option and giving my hip more time to recover.
"Surgery is also an option but the chances of a successful outcome are not as I high as I would like which has made this my secondary option and my hope has been to avoid that. However this is something I may have to consider but let's hope not."
Muguruza withdraws, Serena returns
In the women's draw at Brisbane, Wimbledon champion Garbine Muguruza was forced to retire after collapsing during her match against Serbia's Aleksandraw Krunic with severe cramp.
But 2018 will mark the return of 23-time grand slam champion Serena Williams, who returned to the court at the Mubadala World Tennis Championship in Abu Dhabi at the weekend, less than four months after becoming a mum.
"It's really good to be back on court. It's my first time playing in Abu Dhabi ... first matches back are always super incredibly hard, but it was great and I'm glad I could do it here," Williams said after her 6-2 3-6 10-5 defeat to Jelena Ostapenko.
Williams, currently ranked world No.22, has entered to defend her Australian Open crown.
A 24th grand slam title would see Williams tie controversial Australian Margaret Court for the all-time grand slam lead, women or men.