Horford is out for Thursday's game versus the Bucks due to rest purposes, Taylor Snow of the Celtics' official site reports.
Horford will continue to sit out one leg of Boston's back-to-backs. However, Kristaps Porzingis will return to action, while Luke Kornet and Neemis Queta are candidates to receive increased minutes. Horford should return for Saturday's matchup with Houston.