Boston defenceman Charlie McAvoy remains in the hospital with a "significant injury" to his right shoulder that developed an infection, the Bruins said on Wednesday, a day after he was scratched from the 4 Nations Face-Off.

The statement from head team physician Peter Asnis said McAvoy injured his acromioclavicular (AC) joint in the American round-robin game against Finland on Thursday in Montreal and was treated by the Team USA medical staff.

The pain increased after he returned to Boston, and further testing revealed the infection. Doctors treated the infection and McAvoy is improving, Asnis said.

McAvoy, 27, had been a key contributor to the American team in the international tournament whose big hits on Canadian stars Connor McDavid and Sidney Crosby were credited with setting a tone in the round-robin matchup between the North American rivals.

Thursday's championship against Canada will be at the TD Garden, the Bruins' home ice.

"He's obviously disappointed that he won't have the ability to participate in the championship game. This tournament means a lot to him," U.S. head coach Mike Sullivan, who is also McAvoy's father-in-law, said on Tuesday. "I'm disappointed for him because first and foremost, he's a great kid and he's a terrific hockey player, and I know this meant a lot to him."

McAvoy, who had left shoulder surgery in 2022, is serving as assistant captain on the 4 Nations roster. He missed seven games in January with an upper-body injury and returned to action Jan. 30.

Sullivan identified reigning Norris Trophy winner Quinn Hughes as a possible replacement, but he remained in Vancouver with the Canucks on Tuesday.

WATCH l 3 fights in 9 seconds to open U.S.-Canada game: 

3 fights in 9 seconds opens Canada vs U.S. 4 Nations Face-Off showdown

American Matthew Tkachuk squared off with Brandon Hagel right after the opening faceoff. Brother Brady Tkachuck then fought Sam Bennett. Seconds after play resumed, J.T. Miller and Canadian Colton Parayko dropped the gloves.