Ben Simmons left Saturday's night game against the Orlando Magic with back tightness 4 minutes, 19 seconds left in the first quarter. He did not return.
The 76ers point guard went straight to locker room and was ruled out the rest of the game.
Simmons had four points on 2-for-3 shooting to go with four assists in 7 minutes, 41 seconds of action.
The 2017-18 rookie of the year was having a great start to the season.
Simmons posted his first triple-double of the season and 13th of his career in Thursday's victory over the Chicago Bulls. He had 13 points, 13 rebounds and 11 assists in 34 minutes, making him the first Sixer to post a triple-double in a home opener.
In a season-opening loss to the Boston Celtics, Simmons finished with 19 points, 15 rebounds, eight assists, four steals and two blocks.
Simmons recorded 12 triple-doubles in last year's regular season, the second most by a rookie in NBA history. He also averaged 15.8 points, 8.1 rebounds, and 8.2 assists. Simmons garnered Eastern Conference rookie-of-the-month honors for October/November, January, February, and March/April.
The Australian had posted at least 10 points, five rebounds and five assists in 58 games this season. That's third behind Oklahoma City Thunder point guard Russell Westbrook and Cleveland Cavaliers forward LeBron James.