Montreal defeated Dallas 4-2 on Tuesday night but the game went sour when Shaw hobbled off the ice after a helmet-to-helmet collision with former teammate Greg Pateryn.
Shaw knocked Pateryn down with a big hit along the boards with 11 minutes left, but the Canadiens winger got the worst of it when their heads collided. With Shaw lying on the ice, Pateryn punched him twice in the head.
''Kind of makes you feel sick when you see that,'' Montreal defenseman Karl Alzner said. ''It's like in UFC when the guy keeps going after a knockout. It's unacceptable. You get fired up in the moment and you do things you don't necessarily think through. It's not something you ever want to see.''
Added Jonathan Drouin: ''I thought Andrew's hit was clean. I didn't like the two punches at the end when his head was down on the ice. I think the league might take a look at that one.''
After the hit, Shaw lay motionless for several minutes before getting to his feet. He had to be helped off the ice.
Canadiens coach Claude Julien said team doctors were monitoring Shaw, but he was not taken to a hospital. Julien said Shaw was ''shaken up,'' but did not call it a concussion. Shaw suffered two concussions last season.
''He took a run at me and his head hit mine,'' said Pateryn, who had an assist on Dallas' first goal. ''There's a reason why a guy like that gets four or five concussions a year. His play speaks for itself.''
The Canadiens (26-32-12) scored three power-play goals as they snapped their five-game skid. Montreal had not won since March 2.
Antti Niemi made 36 saves for his fifth victory of the season. Niemi has not lost in regulation since Feb. 14, going 3-0-3 during that stretch. The Canadiens were at home for the first time since a 1-3-2 trip.
Lehkonen tied it 1-all with a wrist shot, blocker side, at 16:31 of the first period.
A four-minute high-sticking penalty to Dan Hamhuis in the second changed the course of the game, with Montreal scoring twice in 35 seconds.
First, Lehkonen beat goalie Kari Lehtonen between the legs from the slot at 8:41. And after Radek Faksa took a tripping penalty to give the Canadiens a two-man advantage, Gallagher scored his team-leading 26th of the season at 9:16.
Scherbak made it 4-2, again on the power play, at 9:26 of the third.
''Especially at this time of the year, with teams pushing for the playoffs, every game is so tight,'' said Galchenyuk, who has eight points in his last eight games. ''One or two power plays can make a big difference. It definitely gave us momentum.''
The game marked Alexander Radulov's return to the Bell Centre. Radulov had not faced his former club in Montreal since signing with Dallas as a free agent in the offseason.
Faksa got Dallas (38-26-6) on the board at 11:48 of the first period as he deflected Pateryn's shot past Niemi. Jamie Benn made it 3-2 with 1:40 remaining in the second. Radulov got an assist on the goal.
The Stars have lost four of five.
''It's bad,'' Radulov said. ''We need points. We're in the playoff race and we didn't get it done. We put ourselves in that position. It's our fault.''
The Canadiens announced during the game that defenseman Shea Weber underwent surgery Tuesday to repair a torn tendon in his left foot. The team expects his recovery to take six months.
Weber is thought to have been injured when he was hit by a shot in the first game of the season. The 32-year-old has not played since Dec. 16.
NOTES: The Stars are two games into a six-game road trip. ... The Stars beat Montreal 3-1 earlier this season in Dallas.
Stars: At the Toronto Maple Leafs on Wednesday night.
Canadiens: Host the Pittsburgh Penguins on Thursday night.
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