The NFL announced the suspension Friday. Coach Mike Shanahan said a month ago that Buchanon would be suspended for the first four games of the regular season, but the coach did not reveal why.
Buchanon re-signed with the Redskins on Aug. 1. He saw limited action during the preseason because the coaches wanted to focus on players who would be available for the first month.
The NFL says the suspension officially begins Saturday. Buchanon will be eligible to return to the active roster on Oct. 3.