Bynum, who has started 19 of Cleveland's 28 games this season, did not travel to Boston for Saturday's game against the Celtics.
"(He) has been excused from all team activities indefinitely. His status will be updated as appropriate," the Cavaliers said in a statement.
The team did not give precise reasons for Bynum's ban and coach Mike Brown would not discuss details ahead of the game with Boston, calling it an "internal matter".
Bynum played seven seasons for the Los Angeles Lakers, starting 300 games, before being traded to the Philadelphia 76ers in August 2012.
He then missed all of the 2012-13 season with knee injuries and signed a two-year contract with the Cavaliers in July 2013.
Bynum averages 8.6 points and 5.3 rebounds this season while featuring in 24 games.
According to an ESPN report, the 2005 first-round draft choice of the Lakers said the Cavaliers were looking to trade him.