Socceroos captain and first-choice goalkeeper Mat Ryan appears in a race against time to lead Australia's campaign at January's Asian Cup after suffering a fractured cheekbone.
Dutch club AZ Alkmaar said on Monday that Ryan, 31, suffered a head injury at training on Sunday, then had surgery that would sideline him for several weeks.
"Mathew Ryan suffered a head injury during training on Sunday," AZ Alkmaar said in a statement on their website, translated to English.
"The Australian international has now undergone surgery for a fractured cheekbone and will be sidelined for several weeks."
Ryan's injury leaves coach Graham Arnold with a massive headache leading into Australia's first group game in Qatar, against India on January 13.
Australia also play Syria on January 18 and Uzbekistan five days later.
The goalkeeper is crucial to Australia's hopes of bettering their quarter-final exit in 2019.
Ryan was a part of Australia's 2015 Asian Cup win on home soil under Ange Postecoglou, the only time the Socceroos have won the tournament.
The Socceroos squad will be selected later this month and Ryan would be a lock for Arnold's 23 if a chance to play at all.
At best, Ryan would be coming into Qatar underdone after his injury and would need to quickly get up to speed.
But there is no clear standout for who would fill in for Ryan, who has 86 caps, if he isn't fit to play.
Australia does not have a clear second-choice goalkeeper given Ryan's stranglehold over the No.1 jersey in recent years.
Mitch Langerak is currently out of the fold after he was contentiously left out of last year's World Cup squad and a recall appears unlikely.
It means Adelaide United shotstopper Joe Gauci looms as the next option given his stellar A-League Men season.
While the 23-year-old is talented, he is inexperienced, with just one cap to his name.
Sydney FC custodian Andrew Redmayne had been a mainstay in squads under Arnold but was dropped for recent World Cup qualifiers after a tough run of form at club level.
Tom Glover has had limited game time at club level with Middlesbrough and he and Charlton Athletic's Ashley Maynard-Brewer are yet to debut.
Danny Vukovic retired from internationals after the World Cup.
Ryan had been in strong club form, playing all 24 of AZ Alkmaar's games this season, recording 10 clean sheets.
