Boomers and NBA centre Aron Baynes has been ruled out of the Olympics after he slipped and fell on the changeroom floor and aggravated a neck injury.
The triple Olympian had hurt his neck on court during a win against Italy on Wednesday, but was then sent to hospital after aggravating it further when he fell in the bathroom soon after.
He remained in hospital for tests and monitoring on Friday and has been ruled out for the rest of the campaign, but is expected to recover in within weeks.
"It became apparent to the medical staff that this was a bit more serious than just an average injury and so as a precaution he was taken to hospital and he's undergoing further tests at the moment," Australian team doctor David Hughes said.
Currently playing for Toronto, Baynes has won an NBA title with San Antonio and established himself as one of the world's most physical forwards.
The 34-year-old's presence has been key in Australia's push towards a maiden international medal.
"I am really disappointed that I can't continue in the Olympics," Baynes said.
"I along with the rest of the team have been working so hard in our quest for an historic Olympic medal and I am gutted that I can't complete the journey with the boys, but I have every confidence that they will get the job done."
His absence from a side lacking any like-for-like replacement could expose the gold medal contenders, especially if they come across Rudy Gobert's France or Spain's Gasol brothers Marc and Pau in the knockout rounds.
Baynes dominated Gobert, the NBA defensive player of the year when they met at the 2019 World Cup and has a score to settle against the Spaniards, who cruelly denied the Boomers silverware at that tournament and Rio's 2016 Games.
Instead Australia will lean on Europe-based centre Duop Reath and the relatively smaller line-up of Jock Landale and Nick Kay to continue their winning ways in Japan.
"It's a tough loss for us," Boomers captain Patty Mills said.
"His presence on the floor and physical play has been a big part of our identity for so long and that will be missed, but it doesn't change our focus and how we go about our business and what we have come to achieve.
"We have always spoken about how important each player's role is, and the impact it can have for the better of our group because of our depth.
"That doesn't change. We've got Baynsey's back. We'll cover for him.
"I have every confidence in this playing group and our focus will not waiver as we strive for that Olympic gold medal."
Australia play their final pool game against Germany on Saturday.
Australian Associated Press