Colin Miller has missed the last two games after suffering a lower-body injury in Boston's win over St. Louis last Thursday, while Kevan Miller left Saturday's game after taking a hit from behind into the boards from Philadelphia forward Jakub Voracek.
Coach Claude Julien said on Sunday that Kevan Miller suffered a concussion, which will keep him out while he goes through the league's concussion protocol.
"It's next man up. That's kind of how it's been all year," John-Michael Liles said after Sunday morning's practice at Warrior Ice Arena. "I was out for six weeks. Zee was out for a bit of time, Quaider was out early in the year, Kevan Miller was out early in the year.
"We've definitely had our fair share of injuries on the back end and I think that speaks to the depth that we have, not only here but some of the guys that have plugged in and come up from Providence.
"We've all kind of played with each other in different roles or different situations in a game. I think everybody's comfortable in that."
The Bruins have used 10 defensemen this season, including Matt Grzelcyk and Rob O'Gara, who are both back in Providence after short stints with the big club.
"I don't think anybody's well equipped for losses, but the thing is we have players that we we've got some depth in that position," said Julien. "So far, we'll knock on wood that it's still good, we still have enough here to get through and hopefully we'll have some guys back sooner than later."
With both Millers sidelined, Joe Morrow - a healthy scratch for every game since Dec. 12 in Montreal - is likely to return to the lineup.
"I try and stay in the best shape I can, practice every day. The hockey aspect of things isn't too far away from me. I haven't played in a game for a long time, so I feel like those mistakes will kind of be inevitable. I'm just going to focus on if I make a mistake, I'm going to play hard and keep it simple."