The forward and defenseman Sami Niku were placed in NHL COVID-19 protocol Thursday and must quarantine for 10 days. Niku also tested positive, according to the Canadiens.
Neither played in a 4-1 home loss to the Colorado Avalanche. They will miss four additional games and could be next available to play Dec. 14 at the Pittsburgh Penguins.
Gallagher has scored 10 points (four goals, six assists) in 23 games this season. Niku has three assists in nine games.
Forward Josh Anderson left the game against Colorado in the second period because of an upper-body injury and is expected to be out 2-4 weeks.
Montreal recalled forward Laurent Dauphin from Laval of the American Hockey League after the game.
