Ben Simmons, recently signed to a five-year, $170 million contract extension with the NBA's Philadelphia 76ers, has pulled out of Australia's exhibition games ahead of the World Cup.

The Melbourne-born star had already withdrawn from the World Cup in China, which tips off on August 31, to better prepare for the NBA season.

And the 23-year-old has now opted out of Australia's two games against the United States in Melbourne and two against Canada in Perth in the tournament lead-up.

"After talking with [Australia] coach Andrej [Lemanis], we both agreed it was better for me to not participate in this year's 2019 World Cup and exhibition games," Simmons said in a joint statement with Basketball Australia late Sunday.

"With our focus being to win a medal at the 2020 Olympics, the Boomers' preparation in the lead-up to the world championships is of the utmost importance.

"Me not playing allows the team to create the chemistry they need to compete at the highest level and qualify for the Olympics."

The top seven finishers at the World Cup automatically make the Tokyo Olympics, with the next 16 having to go through qualifying tournaments.

Simmons was the No.1 ­overall draft pick in 2016, and after injury saw him miss the 2016-17 NBA season he was named Rookie of the Year in 2017-18.

He averaged 16.9 points, 8.8 rebounds and 7.7 assists for the 76ers last season, when he was named an NBA All-Star for the first time.