Penguins players immediately called for medical assistance.
"Listen I feel awful. It wasn’t my intention for that outcome," Thornton said. "I know Brooksie. I’ve gotten to know him over the last several years here. I skated with him in the summer through the lockout. I texted him a couple times. I feel awful. It definitely was not I wanted to see or anybody wanted to see."
Thornton and Orpik became involved after Bruins forward Brad Marchand, while on the ice, took a knee to the head from Penguins forward James Neal, who was skating by him. Neal was assessed a two-minute penalty for kneeing.
Thornton was assessed a match penalty; he appeared to pull Orpik down and punch him while he was on the ice.
"That’s always my job, I guess, to defend my teammates," Thronton said. "But I've prided myself for a long time to stay within the lines. I said, it’s hard for me to talk about right now. I can't say I'm sorry enough. And I'm sure I'll be criticized for saying it, but it's true. I just, I hope he's doing all right. I heard that he's conscious and talking. I'm happy to hear that."
Orpik was taken to Massachusetts General Hospital, where he was alert and conscious, the Penguins announced. Orpik returned from the hospital and will travel with the team back to Pittsburgh, coach Dan Bylsma said after the game.
Thornton will have a hearing with the NHL Department of Player Safety at a to-be-determined date, the League announced Saturday night.
The Bruins said via Twitter he will not travel for a game Sunday against the Toronto Maple Leafs.
"Obviously I made a mistake. I'm aware of it," Thornton said. "I've been told that I'll be having a hearing. And it's hard for me to say much more than ... it was not my intention, I feel awful, I felt sick all game, so ..."
Bruins forward Loui Eriksson left the game after his first shift following a hit from Orpik.
NHL.com Correspondent Matt Kalman contributed to this report.