Boston Bruins defenceman Charlie McAvoy has a left MCL sprain and will be re-evaluated in four weeks, general manager Don Sweeney announced Tuesday. 

McAvoy left Saturday's game against the Montreal Canadiens in the first period with a lower-body injury and did not return. After the game, Bruins head coach Bruce Cassidy said he wasn't sure what caused the injury. 

He did not skate with the team Monday and was seen wearing a knee brace, according to multiple reports, but did participate in the team photo prior to practice. 

The 14th overall pick in the 2016 NHL Entry Draft out of  Boston University, McAvoy was expected to be a Calder Trophy contender at the time of his injury in his first season with the Bruins.

In 58 games this season, McAvoy has seven goals and 25 assists in 22:29 a night. He trails only Zdeno Chara in ice time on the team.

McAvoy was out of the lineup for nearly two weeks earlier this season when he underwent an ablation to correct an abnormal heart rhythm, returning to the lineup on Feb. 3.

The Bruins (41-15-8) have won four straight after Tuesday night's 6-5 overtime victory over the Detroit Red Wings (26-29-11). 

Boston sits five points ahead of the Toronto Maple Leafs for second in the Atlantic Division, but have four games in hand.