By Matt Kalman, CBS Boston

BOSTON (CBS) — Rick Nash isn’t walking through that door.

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At least not yet.

No one knows whether the star forward is going to play in the NHL again. And no one knows if he’d even return to the Bruins if he resumed his career.

So the only known right now, with two weeks until the start of training camp, is that Nash left a hole in the Bruins’ forward lineup and general manager Don Sweeney did not make a move to fill it during the offseason.

Wise guys will say it shouldn’t be too hard to replace Nash because he had three goals in 11 regular-season games after joining the Bruins and three more goals in 12 playoff games. But there’s no denying Nash was clicking with Krejci before suffering a concussion, and the former New York Rangers sniper’s presence in the lineup gave opponents something different to plan for that the Bruins lacked before the February trade.

The competition to play on center David Krejci’s right side (assuming Jake DeBrusk remains Krejci’s left wing) will be one of several training camp battles among forwards next month.

Start with the premise that the lineup will look something like this:

Brad Marchand – Patrice Bergeron – XXX

Jake DeBrusk – David Krejci -XXX

XX – XXX – David Backes

XX – Sean Kuraly – XXX

Before you lose your mind and call me a hack, I left out David Pastrnak not because I project him to get assigned to Providence but because any discussion of the Bruins’ forward battles has to start with where to place Pastrnak.

Obviously, the safest thing to do is leave him up top with Brad Marchand and Patrice Bergeron to form a line that last season averaged 3.13 goals per 60 minutes and allowed just 1.79 (all line combination stats in this story are courtesy of Natural Stat Trick and are for 5-on-5 play only).

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For the regular season, assuming none of the Bruins’ younger players suffer a sophomore slump and a rookie or two steps up the way DeBrusk and Danton Heinen did last season, the Bruins could continue to let the best line in hockey carry them to the upper half of the Eastern Conference.

It would sure make life more difficult on opponents, though, if the Bruins took their four most dangerous offensive players and spread them over two lines. It would also help a rookie or a second-year player to right shot gun with Bergeron and Marchand. A Krejci-Pastrnak pair, joined by DeBrusk or another younger player, would give the Bruins a much better chance at exploiting some of the shallower defense corps in the Eastern Conference.

Last season Krejci and Pastrnak played just 80 minutes together. In that small sample size, they generated 3.75 goals per 60 minutes and allowed just 2.27 goals allowed per 60.

There’s no telling what the early-camp China trip is going to do to the Bruins’ lineup combinations, but trying to get Krejci and Pastrnak to click should be a priority for coach Bruce Cassidy.

Should Pastrnak join Krejci full-time, that would leave open that right side of Bergeron’s line. Anders Bjork held that spot for 53 minutes last season and fared well (4.46 goals for per 60 vs. 1.1 goals against). He’s just returning from injury so he could be rusty early in camp. That could open up a chance for Heinen to get major minutes in a role he would probably enjoy because of his responsible play in the defensive zone. But Marchand and Bergeron seem to succeed most when they have a burner as their third member.

Ryan Donato’s one of the many candidates for third-line center. The Bruins, however, have to decide if he can handle all that responsibility or if he’d be better off on the wing. If he starts out on the wing, he could be a fit with Bergeron or Krejci, although both spots would require him to play his off side, which could limit his speed and affect his defensive play. With so much depth, the Bruins might be better to limit the number of challenges they throw at Donato out of the gate.

With David Backes on the right wing of the third line, the Bruins might be able to survive Donato or another rookie playing in the middle the way they got by with Ryan Spooner there. But the Bruins were at their best with Riley Nash centering Backes and Heinen, so that could open up room for a more experienced, bulkier center like Sean Kuraly or Chris Wagner. Neither, however, have the offensive acumen that Nash showed last season. In fact, Riley Nash could prove to be the more difficult Nash to replace.

You throw in Joakim Nordstrom, along with rookies Jack Studnicka, Trent Frederic and Jakob Forsbacka Karlsson and the Bruins have a lot of players capable of centering the bottom two lines. And Noel Acciari has played center although, like Wagner, he’s seemed better suited for the wing in the NHL.

One would expect Studnicka to get a long look after the Bruins’ brass crowed about him so much this offseason. They might even consider giving him a nine-game regular-season audition before making a final decision on his status. There’s no shame in Frederic getting a full AHL season the way DeBrusk and Heinen did two years ago. And Forsbacka Karlsson could also benefit from going to Providence and dominating to force the Bruins’ hand.

The best thing going for Cassidy and Sweeney is that aside from Backes, none of the Bruins’ bottom-six forwards are making the type of money that guarantees them a job. This is going to be a competition in the purest sense of the word. The best five guys that don’t crack the top six are going to play in Boston’s bottom six.

May the best men win.

Read: Defense & Goaltenders

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