Perhaps stirring the pot ahead of a rematch with the Penguins on Sunday afternoon, Carbonneau questioned why Sheldon Souray got seven penalty minutes and an ejection while Armstrong got none for going to Koivu's defence.
"I know it was legal, he hit him with his shoulder, but when a guy's battling one-on-one and (another) guy comes from a blind spot and hits him, I don't like that," said Carbonneau said. "It should have been called.
"And I don't see how they got seven minutes on the power play out of that. It was definitely a cheap shot, I'm not afraid to say it."
He said general manager Bob Gainey planned to discuss the incident with league officials.
Nearly five minutes into the second period of the Penguins' 5-4 shootout win in Pittsburgh on Thursday night, Koivu was skating out from behind the net when Armstrong came flying in for a hit.
Koivu manged to swerve and avoid some of the impact, but was knocked over. Souray went after Armstrong, knocked him to the ice and threw punches.
Referees Francois St. Laurent and Don Koharski slapped Souray with an instigator minor, a fighting major, a misconduct and a game misconduct.
The Canadiens were upset that Armstrong got no penalty, even though he dropped his gloves and looked to have thrown at least one punch.
The Penguins scored twice during Souray's penalties, including once with a two-man advantage, but Montreal countered with one of its two short-handed goals in the game.
Carbonneau said Souray did the right thing by standing up for his teammate, despite the penalties, and said he hoped other Canadiens will do the same if it happens again.
Curiously, Carbonneau gave Koivu and Souray a day off practice Friday, even though neither is injured.
Besides that, Carbonneau called it "a good game" with plenty of playoff-like intensity.
On the opening face-off, Montreal centre Maxim Lapierre looked to have butt-ended Sidney Crosby in the stomach. Crosby got him back moments' later by tripping Lapierre on a face-off. Neither infraction was called.
The Canadiens play host to the New York Islanders on Saturday afternoon and the Penguins on Super Bowl Sunday.