MONTREAL -- Montreal Canadiens right wing Brendan Gallagher will have surgery Monday on two fractured fingers on his left hand and will be out indefinitely, coach Michel Therrien said after a 4-2 win against the New York Islanders at Bell Centre on Sunday.

Gallagher was injured blocking a slap shot from Islanders defenseman Johnny Boychuk at 12:34 of the second period.

"Every time you lose a player that has an important role on any team, it's always a huge loss," Therrien said. "He was playing his best hockey, obviously. He's progressing every year, he's still a young player. It's a big loss, but what are we going to do? We can't feel sorry for ourselves. That's the way it is."

Gallagher ranks third on the Canadiens with 19 points (nine goals, 10 assists), one behind linemates Tomas Plekanec and Max Pacioretty, who are tied for the lead with 20.

With nine goals in 22 games, Gallagher was on pace to surpass 30 goals for the first time in his NHL career after scoring 15 goals in 44 games as a rookie in 2012-13, 19 in 81 games in his second season, and 24 in 82 games last season.

Cameras caught images of Gallagher's mangled left ring finger as he went back to the bench.

"It was pretty gross," Boychuk said.

Boychuk still appeared to be affected by the sight of his shot striking Gallagher in the hand after the game. He has one of the hardest shots in the NHL, and said he got all of the one that struck Gallagher as he kneeled down in front of it.

"Oh yeah, that would hurt," Boychuk said. "I mean, it's a one-timer right on his finger, so I don't think it's good."

Gallagher dropped his left glove and his stick as soon as he was struck, but got up, grabbed his stick by the blade and attempted to get back in the play as the Islanders controlled the puck in the offensive zone. With one glove on his hand and holding his stick the wrong way, Gallagher skated somewhat aimlessly for a few seconds before retreating to the Canadiens bench, throwing off his other glove and heading straight back to the dressing room.

Boychuk gathered Gallagher's gloves at the next stoppage and brought them back to the Canadiens bench to hand them to backup goalie Mike Condon.

"That was definitely not encouraging seeing that," Pacioretty said. "He's a warrior. He plays through anything and he stayed out there on that shift and it says a lot about his personality and his character. I don't know the extent of what it is, but it shows he's a warrior, and we knew that before. We knew what he was made of. We're going to miss him a lot if he misses any time."

The injury to Gallagher is the second major one to hit the Canadiens this season; goaltender Carey Price returned from a nine-game absence to defeat the Islanders twice in three days. The Canadiens went 5-2-2 in Price's absence, and Therrien is hopeful the Canadiens can have similar results without Gallagher.

"We lost Carey Price and that was a big loss too," he said. "But we still found a way to be competitive and to be successful and that won't change."

One of the major reasons why the Canadiens had 110 points last season was them avoiding major injuries to significant players.

Already this season, in addition to Price and now Gallagher, defenseman Alexei Emelin and forwards Torrey Mitchell and Devante Smith-Pelly have missed time due to injury. Pacioretty was injured training in the offseason and it was thought he might miss the start of the regular season, but he came back in time and hasn't missed a game.

Gallagher is among the Canadiens' most important forwards, often used as a catalyst by Therrien to get a struggling line going and thriving on the right side of the top line in his first season as an alternate captain. His ability to get to the net, frustrate opposing defensemen and goalies and retrieve loose pucks on the forecheck is unique and extremely valuable.

Losing him could create a domino effect throughout the forward group. Therrien will look for a way to replace what he brings to the Plekanec line. That won't be easy because there are few players in the NHL who can do what Gallagher does.

"Obviously he's a big part of our team but we have to be resilient and we have to carry on even if we're going to be missing him for a while," Price said. "We have a lot of depth on our team. He's a leader on our team. We're going to miss him, however long that's going to be."