The German defender was shown his fifth yellow for pulling down Nemanja Nikolić in the 19th minute.
Wagner missed two games earlier this season after serving a red card suspension and getting an extra game from the Disciplinary Committee. Ray Gaddis started at left back in his absence. He was a late scratch last week against Real Salt Lake because of injury and replaced in the lineup by Fabinho.
Montreal entered the game Saturday six points behind the Philadelphia Union in fifth place in the Eastern Conference. The game will be played at Stade Saputo in Montreal.