Parros was knocked unconscious early in the third period after his face slammed into the ice during the scrap. Parros spent several minutes motionless on the ice before he was taken off on a stretcher.
"Medical update on George Parros: he was released from the hospital, suffered a concussion, will be out indefinitely," the Canadiens said Wednesday on their Twitter feed.
Parros fell hard on his chin while attempting to punch Orr, who was tugging at his jersey. It was their second fight of a physical game, which the Maple Leafs won 4-3.
It was the first game in a Montreal uniform for Parros, who joined the Canadiens last summer after one season with the Florida Panthers.
The incident reignited the debate about whether fighting should be a part of the game. Many players say yes.
"Fighting is not going anywhere in the game," Vancouver defenceman Kevin Bieksa said. "It will always be a part of the game. We'll play with a tennis ball before we take fighthing out of the game."
Jets centre Bryan Little said he has "no idea what (hockey) would look like without it."
"As far as I can remember it's been a good way for the players to kind of police the game themselves," he said at practice in Winnipeg on Wednesday.
Defenceman Zach Bogosian said much the same thing.
"If they take fighting out of the game it will be a whole different dynamic and it won't be the same," he said. "Fighting should always be in hockey, not matter what, because you'll get guys running around that play a lot tougher than they normally would. It's good, it keeps everyone honest."
Winnipeg tough guy Chris Thorburn called the Parros incident a "freak accident."
"Hopefully the results of fights going into the future aren't like that," he said.
Canucks coach John Tortorella said he's seen enough of the "staged fighting," but said that dropping the gloves will always be part of the game.
"I think we've lost ourselves a little bit in how hard the game should be played, how honest the game should be," he said. "I think when there's honest, hard-hitting action there's going to be fights, but that's when the fights should take place. I always go back to 'I think the players need to police the game.' I think we've not allowed them to police themselves. We have too many things going on other ways where we've lost a little bit of the honesty."
Parros was drafted by the Los Angeles Kings in the eighth round (No. 222 overall) of the 1999 NHL Entry Draft.
He made his debut with the Kings in 2005-06 and later played for the Colorado Avalanche and Anaheim Ducks.
The 33-year-old native of Washington, Pa., had two points (1-1) and 57 penalty minutes in 39 games with Florida last season. He has 35 points (18-17) and 1,027 penalty minutes in 453 career NHL regular-season games.
— With files from Canadian Press reporters Scott Edmonds in Winnipeg and Joshua Clipperton in Vancouver.