BOSTON — Al Horford was treated for left knee soreness and left hamstring tightness Thursday and was held out of the game against the Boston Celtics at TD Garden.

The 76ers center did, however, participate in the team’s morning shootaround. He also tested his knee and hamstring during pregame warmups, but was ruled out. The matchup was scheduled to be Horford’s first game back in Boston since leaving the Celtics this summer to sign a free-agent deal with the Sixers.

The 33-year-old spent three seasons with the Celtics, averaging 13.5 points, 7.0 rebounds, 4.6 assists, and 1.2 blocks. He garnered his fifth All-Star selection in Boston during the 2017-18 season. His other four selections came as a member of the Atlanta Hawks.

Through 23 games with the Sixers, Horford is averaging 13.8 points, 6.8 rebounds, 3.9 assists, 1.1 steals, and 1.0 block.

Meanwhile, the team reassigned Zhaire Smith its G League affiliate, the Delaware Blue Coats. The laceration on his right leg is healing, so the second-year player is ramping up his on-court activity. He’s expected to return to action Saturday in the Blue Coats’ game against the Raptors 905 in Ontario.

Smith has yet to play for the Sixers this season. He’s averaging 12.7 points, 4.0 rebounds and 1.7 assists through seven games for the Blue Coats.