Former world number one Andy Murray and Japan's Kei Nishikori pulled out of the Australian Open Thursday as a host of top names battle to be fit for the year's first Grand Slam.

Murray, 30, had failed to recover from a hip injury sustained last year and has not played since losing in the Wimbledon quarter-finals last July, while Nishikori has been on the sidelines since August due to a torn tendon in his right wrist.

"Sadly I won't be playing in Melbourne this year, as I am not yet ready to compete," the three-time Grand Slam champion Murray said in a statement.

"I'll be flying home shortly to assess all the options but I appreciate all the messages of support and I hope to be back playing soon."

Murray, who earlier withdrew from the Brisbane International, did fly from Queensland to Melbourne, but only to catch a connecting flight back to Europe, the national broadcaster ABC reported.

- 'Hard decision' -

Australian Open tournament director Craig Tiley said he respected what was a "very hard decision for Andy."

The loss of the Scot, who may now opt for surgery on his hip, came with injury clouds hanging over a who's who of stars before the Open begins on January 15

World number one Rafael Nadal and six-time Australian Open champion Novak Djokovic remain huge doubts having yet to play a competitive match this year.

Nadal, the reigning French Open and US Open champion, pulled out of Brisbane at the weekend with a knee injury but said he still intends to play at Melbourne Park.

Former world number one Novak Djokovic has not played since a right elbow issue forced him to quit Wimbledon in the quarter-finals.

He cancelled scheduled appearances in Abu Dhabi and Doha but intends to test the injury next week at two warm-up events in Melbourne before deciding whether to embark on a tilt at a record seventh Aussie title.

"Novak is travelling to Australia where he will take part in two exhibition tournaments," said a statement on 12-time Grand Slam winner's website early Thursday. "After the two events, the decision will be made about his participation."

World number eight Jack Sock joined the growing injury list when he injured his hip at the Hopman Cup in Perth on Tuesday.

Former champion Stan Wawrinka and Canada's Milos Raonic are also returning from injuries but intend to play in Melbourne.

On the women's side of the draw there are question marks over the fitness of defending champion Serena Williams, who has not played competitively since giving birth four months ago.

- 'Game becoming more physical' -

And British number one Johanna Konta, a semi-finalist in Melbourne two years ago, retired from her Brisbane quarter-final Thursday with a right hip injury and was not sure if she would defend her Sydney International title next week.

"Hips take a massive beating," Konta said.

"Obviously, our game is becoming more and more physical and the demands of the tour as well, week-in and week-out, is becoming more demanding."

Earlier in the week Wimbledon champion and world number two Garbine Muguruza was forced to retire at Brisbane with severe leg cramps, though the Spaniard two-time Grand Slam winner on Thursday accepted a wildcard to play in Sydney.

US Open champion Sloane Stephens pulled out of Brisbane before the tournament to rest a troublesome knee but is entered for Sydney.

And upcoming French star Caroline Garcia, who enjoyed a breakthrough season in 2017 rising to eight in the world, retired in tears with back pain from the same event on Sunday.

Asian number one Nishikori said his rehab had been "going well but I am just not ready 100 percent to come back yet in best of five set matches".

The 28-year-old made the fourth round of the Australian Open last year, losing in five sets to eventual champion Roger Federer, who at the age of 36 appears to be one of the few top names to be fully fit

Source: AFP