By Matt Kalman, CBS Boston

The Bruins are in the same position as almost every other NHL team heading into the expansion draft on June 21 — they’re in danger of losing a useful player.

Most of the attention in terms of Bruins general manager Don Sweeney has focused on the defense core, where the Bruins will be able to protect three players if they, as expected, opt for the 7-3-1 protection list (seven forwards, three defensemen, one goaltender).

Captain Zdeno Chara has to be protected because of his no-movement clause and Torey Krug has to be protected because you’re not losing a player of his caliber for nothing. I’m not telling you anything that you don’t know when I explain that the third protected defenseman would come from a group of Adam McQuaid, Kevan Miller and Colin Miller, and that McQuaid will almost definitely be exposed — leaving the Millers vying for the last protected spot.

The easy thing for Vegas Golden Knights general manager George McPhee to do will be to just ignore Sweeney’s calls and pluck a Miller off their roster. Of course, McPhee could be looking to sweeten his coffers even more, and Sweeney should be aggressively trying to divert McPhee’s eyes.

Even though every team is in the same boat, the worst thing for a team to do is lose players for nothing, especially on defense. There haven’t been too many seasons when the Bruins started training camp and ended training camp with the same six or seven defensemen healthy and ready to go. Depth is paramount for teams looking to get off to a strong start and to make it through the season and stay in championship contention. The Pittsburgh Penguins, who are one win away from winning the Stanley Cup, have been down to their eighth, ninth and even 10th defenseman at points during their postseason run.

If the Golden Knights could be coerced into taking McQuaid, the Bruins would lose the least valuable of their draft-eligible defensemen, and they’d free up $2.75 million in salary-cap space. But they’d be losing a veteran with toughness and smarts who holds his own as a third-pair defenseman and, when he’s not among the injured defensemen (so often he is the injured party), has proven he can play up in the lineup at 5-on-5 for stretches and is always an important penalty killer.

When you consider the added depth Charlie McAvoy has provided the Bruins and what they should have at their disposal this season, with Rob O’Gara, Jeremy Lauzon and Jakub Zboril possibly ready to push for a job, losing McQuaid might be viewed as a minor bruise to the depth chart, but there are a lot of ifs when looking at the up-and-coming group. Even the amazing McAvoy isn’t guaranteed to come back in the fall ready to be a regular in the lineup, and the others may need either more AHL seasoning or a long run in the AHL during their first season of pro hockey. Even rookie standout Brandon Carlo could conceivably take a step back as a NHL sophomore. The Bruins have to cover themselves

And that brings us to the Miller vs. Miller debate. While the easy thing to say is that the 24-year-old Colin, who’ll probably be making a little more than $1 million on his next contract (he’s a restricted free agent) is the must-keep over Kevan, who’s 29 and makes $2.5 million, it’s actually a more difficult decision than some think. The Bruins’ mandate now that they’ve made the playoffs after a two-year drought is to do be more competitive in the regular season and postseason next year. Kevan Miller provides them with a stabilizing presence that can play up and down the lineup and play both left and right side. Based on his improved play after the coaching switch to Bruce Cassidy, Kevan Miller is one of the better bargains around.

Colin Miller has potential but even with Cassidy’s cajoling him, he struggled to find consistency. He not presently a top-four defenseman and if he does improve there’ll still be no room for him if enough of the prospects pan out the way Boston wants. He’s not much more than a cheap placeholder, but without the experience of a Kevan Miller to tutor the younger players. The Bruins are not going to remain competitive with three or four first- or second-year players on defense at the same time. They need a balance. They also need assets and Kevan Miller’s trade value when it comes time to clear roster space might be higher in the months and years ahead than Colin’s depending on Colin’s development.

The bottom line is if Sweeney wants to divert McPhee’s eyes elsewhere, it has to be from his defensemen to the forwards, where there are some expendable players, and not to a specific defenseman. Defense depth is too valuable to let the Golden Knights get their paws on anyone.

Matt Kalman covers the Bruins for CBSBoston.com and also contributes to NHL.com and several other media outlets. Follow him on Twitter @MattKalman.