NBA officials made the announcement a day before he was scheduled to play in the Sixers' season opener in New Orleans on Wednesday, CBS Philly reports.
Head coach Doc Rivers invited Simmons to participate in a defensive drill, but Simmons declined, sources told a reporter for The Athletic.
When Rivers asked him a second time, he refused again. That's when Rivers told Simmons he should go home, and Simmons reportedly dropped the ball and left.
Simmons is allowed to return for the next practice, CBS says.
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