"I will still be heading back home to Australia to host my camps as well as train and play with the Boomers in the upcoming Exhibition Games," Simmons wrote on Twitter, referring to contests against the United States in Melbourne next month. "I'm really excited about the talent we have on the Boomers squad, especially moving closer to 2020 where I will be honored and humbled to represent my country on the world's biggest sporting stage at the Olympics in Tokyo.

"Ultimately, we decided it was best that I used the time in September to return to Philadelphia to acquaint myself with my new teammates and prepare for the upcoming NBA season."

Simmons and the 76ers agreed Monday to a five-year, $170 million maximum contract extension, which was confirmed by his agent Rich Paul. The Sixers also made an official announcement Tuesday while not disclosing the terms.

Simmons opened his Twitter post by writing, "I want to say thank you to everyone who reached out to congratulate me on the extension with the 76ers. Philly means so much to me, and I'm already excited for next season."

Simmons, who turns 23 on Saturday, is coming off an All-Star season in which he averaged 16.9 points, 8.8 rebounds and 7.7 assists in 79 games for the Sixers.

He was born in Australia and lived there until he moved to the United States in 2013 to play high school basketball. He was the first pick in the 2016 NBA Draft and the winner of Rookie of the Year honors in 2017-18 after sitting out a season due to injury.

Simmons talked after last season about playing in upcoming events for the Australian national team, known as the Boomers.

Team Australia will compete in four warmup games, including two against USA Basketball, in Melbourne in August ahead of the World Cup.

The Boomers finished fourth in the 2016 Rio Olympics.