Williams won't play in Tuesday's game against the Wizards due to left knee injury management, per Casey Holdahl of the Trail Blazers' official site.
Tuesday is the back end of the Trail Blazers' back-to-back set, so it's not a shock to see the oft-injured big man receive a maintenance day. The expectation is that Williams will be available to play Friday against the Knicks. Portland is down to rookie first-rounder Yang Hansen as the top backup center behind Donovan Clingan.