NBA's Simmons quits Australia's Olympic basketball squad

Ben Simmons withdrew from Australia's Olympic basketball squad Tuesday, with officials saying he was having a "rough time" in the NBA and wanted to focus on improving his skills.

The 24-year-old guard was heavily criticised for his wayward shooting when the top-seeded Philadelphia 76ers were bundled out of the NBA playoffs by the unfancied Atlanta Hawks earlier this month.

National coach Brian Goorjian said he and the rest of the squad supported Simmons' decision and hoped he would represent Australia's Boomers in the future.

"It is a pretty rough time for him right now and I know it (the Tokyo Olympics) is something that he wanted to do, but the timing just hasn't worked," Goorjian said in a statement.

"The best thing for everybody right now is for him to go on and develop that skill package and improve in a couple of areas for his next season in the NBA, but the Boomers are always here for him."

Australia are ranked third in the world heading into the delayed Tokyo 2020 Olympics next month and Simmons was expected to be a linchpin in their quest for a first Games medal.

However, he has never played for the national team, prompting former Boomer and NBA star Andrew Bogut to question his commitment.

"To be too blunt, if you need to be recruited to play for your national team and have a presentation about why you should play, you shouldn't play," Bogut told Fox Sports Australia after the latest withdrawal.

"It's bittersweet. We don't really know what he can bring because he's never brought it for the national team."

Veteran Patty Mills, who is expected to lead Australia in Japan, said Simmons would face no criticism from within the squad.

"We support each other through the good, bad and ugly, whatever it may be, and Ben isn't an exception to that," he said.

"No matter what he does, myself and the team will continue to support him because this is a safe place."

Simmons' future with the Sixers is under a cloud, with US media reporting the Eastern Conference franchise want to offload him.

The Boomers will go to Tokyo also without former Dallas Mavericks swingman Ryan Broekhoff, who quit last week citing mental health issues, and centre Isaac Humphries, who has a foot injury.

The 16-man Australia squad are currently assembling for training in Las Vegas, where they will be cut to 12 early next month before playing exhibition matches against the United States, Nigeria and Argentina.