Roussel was assessed a five-minute major penalty for cross-checking and thrown out early in the first period of Dallas' 5-3 win Tuesday night.
Roussel turned toward McQuaid after sidestepping his attempted check along the boards, and McQuaid was taking off his gloves in anticipation of a fight when Roussel hit him while holding his stick.
McQuaid went to the locker room but returned to the game.
The suspension announced Thursday will cost Roussel $21,505. The third-year player has 11 goals and 11 assists in 54 games.
The Stars host Florida on Friday before a trip to Colorado on Saturday.