An unusually long list of injuries and illnesses, which has already seen withdrawals by the likes of Serena Williams, Novak Djokovic and Andy Murray, has left the door wide open for lesser contenders at the Australian Open.

Here's a 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.

Rafael Nadal

A knee injury forced the Spanish world No 1 out of the warm-up Brisbane International, but he has arrived in Melbourne and is 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

His 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 No 5 pulled out of the warm-up Qatar Open just hours before his semifinal 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 No 3 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.

Stephens had a remarkable 2017 after almost a year out with a left foot injury.

Johanna Konta

A semifinalist 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.

Kvitova missed last year's Australian Open after being attacked by a knife-wielding home invader in the Czech Republic.

Julia Goerges

The German, ranked No 12, withdrew from the Sydney International just hours after beating Caroline Wozniacki to win the Auckland Classic on Sunday, citing a right knee injury.

Agence France-presse