The Bruins could be without Casey Mittelstadt for a little while.

Boston’s second line left wing/center hasn’t been placed on injured reserve but isn’t expected to play this week - beginning Tuesday vs. Toronto at TD Garden - with a lower-body injury.

“He’s still week-to-week but he’s doing better than we expected,” Sturm said on Monday. “So hopefully we can get him on the ice as soon as possible.”

Mittelstadt’s absence means that Boston is without its top two opening night centers. Pavel Zacha is now centering the second line with Providence call-up Alex Steeves on the left wing.

Mittelstadt had four goals and five assists before the injury. He took a big hit in Boston’s win over Ottawa on Thursday but returned to the game.

Johnny Beecher and Charlie McAvoy, who each missed Satur

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