Orpik was pulled to the ice and punched twice in the head by the Boston Bruins' Shawn Thornton in a crowd of players and officials during a stoppage in play at 11:06 of the first period of the Bruins' 3-2 win at TD Garden.
Thornton, dressed in a suit and speaking quietly in front of his locker after the game, said he was sorry for what happened.
"It's hard for me to talk about right now. I can't say I'm sorry enough. I'm sure I'll be criticized, but it's true," he said. "I felt awful. It wasn't my intention. I know Brooksie. I've gotten to know him the last seven years here. I skated with him during the lockout. I texted him a couple of times. It's not what I wanted to see or anyone to see."
Thornton was handed a match penalty and has been told he faces a disciplinary hearing.
Penguins coach Dan Bylsma believes Orpik could be concussed.
"I think he was out on the ice for a period of time, so I think that means he's got a concussion, for sure," he said.
This rematch of last season's Eastern Conference finals -- which the Bruins swept in four games -- was a physical game from the opening puck drop. On the first shift of the game, Orpik knocked the Bruins' Loui Eriksson from the game with a major check.
Eriksson had trouble getting to his feet, but made it to the bench before being taken to the locker room. He did not return to the game and the Bruins announced later that he had a concussion, his second in a five-week span.
Chris Kelly was also hurt, suffering an injury on a slash. Neither Eriksson nor Kelly will travel with the team on its upcoming four-game road trip.
After Eriksson left, Thornton attempted to fight Orpik, but the Pittsburgh defenseman did not oblige. Thornton was given two minutes for roughing.
With the game tied 1-1, the Bruins' Brad Marchand was on the ice as the Penguins' James Neal skated by and appeared to intentionally knee Marchand in the head. As Marchand lay on the ice, play was stopped as he was tended to by a trainer.
Thornton then skated toward Orpik, grabbed him and threw him to the ice before he started to punch him.
Orpik's eyes were open but he was clearly out of it as he was tended to by trainers from both teams and a Bruins team doctor. After nearly 10 minutes, Orpik was taken off the ice on a stretcher.
"I feel awful. It wasn't my intention," Thornton said. "I know Brooksy and have gotten to know him over the last seven years. I skated with him in the summer, through the lockout and texted him a couple of times. I feel awful. It's definitely not what I want anyone to see.
"... It's always my job, I guess, to defend my teammates. But I prided myself for a long time to stay within the lines. It's hard for me to talk about right now. I can't say 'I'm sorry' enough."
When asked if he had an opinion on being kneed in the head by Neal, all Marchand said was: "No."
After the game it was announced that Neal will have a discipline hearing.