Dunne was placed on waivers by the Capitals for the purpose of reassignment to AHL Hershey on Friday.
Dunne made a career-high 34 regular-season appearances with the Sabres last year and recorded a goal, three assists, 40 hits, 38 PIM and 16 blocked shots while averaging 9:29 of ice time. After signing a one-year deal with the Capitals during the offseason, he'll head to the minors to begin the regular season, assuming he clears waivers.