Hartenstein (Achilles) is out for Monday's game against Houston, Fred Katz of The Athletic reports.
Hartenstein's next opportunity to take the court comes Wednesday against Orlando. Taj Gibson started in Saturday's 125-111 loss to the Pacers in Hartenstein's place, but the Knicks could lean more heavily on Precious Achiuwa and Jericho Sims (illness) to cover the minutes at center Monday.