Philadelphia Flyers defenseman Matt Niskanen is suspended for Game 6 of their NHL playoff series against Montreal for breaking the jaw of Canadiens forward Brendan Gallagher with a crosscheck, the NHL Department of Player Safety announced Thursday.

The Canadiens said Gallagher required surgery and will not return to the series. Game 6 is scheduled for Friday night in Toronto.

The incident happened at 14 minutes, 52 seconds of the third period in Game 5 on Wednesday, with Montreal on a power play. As Niskanen was playing the puck, Gallagher crosschecked him to create a turnover. Niskanen then delivered a crosscheck to Gallagher, striking him on the face and breaking his jaw. Gallagher went to the Montreal bench with a mouth full of blood.

The Flyers' argument in Thursday's NHL Player Safety hearing was that Niskanen did not intend to strike Gallagher in the head but rather his upper body, and that this play is commonplace when defenders are moving players off the puck in a game, with punishment usually handled by the on-ice officials rather than Player Safety.

There also was the issue of Gallagher's body position. Player Safety does factor in the incidental body position of the player on the receiving end of the illegal play. Niskanen came down with his stick in an effort to get Gallagher's shoulder, rather than targeting the head. Gallagher was crouched down and attempting to play a bouncing puck when the blow was delivered.

Flyers coach Alain Vigneault defended Niskanen, who had been fined only once previously in his NHL career.

"In my estimation, Gallagher got up and seemed fine. He was talking to the referees. The whole time that he was on the bench, he was talking to our players for the rest of the game," Vigneault said Thursday. "Gallagher is a very competitive player, but I don't think it's Nisky's fault. [Gallagher] might not be as tall as the other guys, but he competes as big if not bigger than anybody else."

The Canadiens applied pressure on the NHL during its deliberation by releasing injury information on Gallagher and publishing their own angle of the incident on social media.

NHL Player Safety uses injuries on a play to determine the length of suspension, rather than whether there should be a suspension.