McAvoy, 20, hasn't played since Oct. 18, missing four games. According to reports, the move to IR is retroactive to the date of his injury, meaning his return won't be significantly affected.
The Bruins had a need for a roster move with defenseman Torey Krug being activated for the first time since suffering an ankle injury during their preseason. Krug, who played Tuesday night against the Hurricanes, had 59 points last season.
McAvoy still leads Bruins defenseman with six points after putting up 32 points last season. He missed 19 games in 2017-18, including sitting for a stretch when he had a procedure to correct an irregular heartbeat.