An unusually long list of injuries and illnesses could take its toll on the Australian Open, which has already seen withdrawals by Serena Williams and Andy Murray.
AFP Sport gives the rundown of who has been struggling in the lead-up to the first Grand Slam of the year:
Novak Djokovic
Six-time Melbourne champion has been sidelined since Wimbledon in July with a right elbow injury, although the Serb intends to play exhibitions this week and insists he "is ready".
Rafael Nadal
A knee injury forced the Spanish world number one out of the warm-up Brisbane International, but he has arrived in Melbourne and expected to be a leading contender.
Stan Wawrinka
The 2014 champion is returning after two operations on a knee cartilage injury. Pulled out of Abu Dhabi exhibition appearance late last month.
Milos Raonic
Calf and wrist problems kept the tall Canadian out of action since last October. Played the Brisbane International, but was bundled out by a wildcard.
Nick Kyrgios
Leg was strapped at the Brisbane event which he said related to fluid on the back of his left knee. It didn't seem to trouble Australia's big hope, who won the tournament.
Jack Sock
The American retired from a match at the Hopman Cup with an injured hip, but returned two days later when he lost to Roger Federer.
Dominic Thiem
The Austrian world number five pulled out of the warm-up Qatar Open just hours before his semi-final with flu and a fever.
Jo-Wilfried Tsonga
The 2008 Australian Open runner-up withdrew from the Qatar Open before it started with a wrist injury.
Garbine Muguruza
World number three retired from Brisbane after collapsing with severe leg cramps. She is playing the Sydney International this week.
Sloane Stephens
The US Open champion withdrew from Brisbane to rest a troublesome knee and was knocked out of Sydney in the first round. Had a remarkable 2017 after almost a year out with a left foot injury.
Johanna Konta
A semi-finalist in Melbourne two years ago, the Briton's Brisbane campaign ended early when she retired with a right hip injury.
Caroline Garcia
The rising French star retired in tears from Brisbane with a back injury in the opening round, saying she could barely move.
Petra Kvitova
The two-time Wimbledon champion pulled out of Brisbane with a viral illness. She missed last year's Australian Open after being attacked with a knife near her Czech home.
Julia Goerges
The German, ranked 12, withdrew from the Sydney International just hours after beating Caroline Wozniacki to win the Auckland Classic on Sunday, citing a right knee injury.