Anne-Marie Sorvin-USA TODAY Sports

The blue line for the Boston Bruins had suddenly become a Mash unit with three regulars out for their big divisional tilt against the Toronto Maple Leafs on Thursday night at TD Garden.

Prior to an optional skate on Thursday morning, Boston Bruins head coach Jim Montgomery confirmed that veteran defenseman and penalty kill specialist Derek Forbort will not play against the Maple Leafs.

“[Forbort] is out tonight…he is day to day, but he is not going to play tonight,” Montgomery told the media.

Forbort joins defenseman Matt Grzelcyk – who is on long-term injured reserve with a shoulder injury – and Charlie McAvoy, who will be serving the first game of a four-game suspension. In their place in the lineup will be rookie Mason Lohrei and defensemen Ian Mitchell and Parker Wotherspoon.

As for how the Boston Bruins will compensate for the loss of Derek Forbort on the penalty kill, it appears the Bruins will use a committee of Lohrei and Wotherspoon.

“I think it’s going to be a combination of Lohrei and Wotherspoon’s going to play,” Montgomery said of the two newbies. “They’re both left shots, so. …both did it pretty well in the preseason so. …I guess Joe (assistant coach and penalty kill coach Joe Sacco), of who he’s going to deploy there, but it’s going to be one of those two.”

Throughout the preseason, Lohrei was into the mid-twenties or above in minutes played, and while this will be his first NHL game, Montgomery said he won’t be afraid to let the 22-year-old rookie rack up the minutes again.

“Being his first preseason game, he’s going to be excited and raring to go,” Montgomery said. “It just depends on how the game plays out with special teams, and also who’s going, how we’re playing, it will depend on how we manage his minutes.’

Here’s what the blue line will look like for the Boston Bruins to start the game tonight:

Hampus Lindholm-Kevin Shattenkirk

Mason Lohrei-Brandon Carlo

Parker Wotherspoon-Ian Mitchell

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