With both players were chasing the puck, Shelley shoved McQuaid and knocked him off his skates. The Bruins defenceman narrowly avoided hitting the boards headfirst.
McQuaid stayed down for several minutes and had to be helped off the ice with the assistance of teammates on each arm.
Shelley, who was given a five-minute major and a game misconduct on the play, apologized to McQuaid on the ice and in the hallway outside the dressing rooms.
"When I was coming off the ice, he was waiting for me there," said McQuaid, who returned in the third period. "He said he was sorry and he didn't mean to, so I've just got to take what he says."
McQuaid said he had the wind knocked out of him and said it was not a head injury.
"They did a few tests and I got checked out and everything," he said.