BUFFALO – Don Sweeney’s mission for this weekend, should he choose to accept it, is to come away with a top-four defenseman capable of transitioning the puck for a Bruins team badly in need of that exact kind of impact player.

But it’s not just about simply acquiring the established blueliner that will add legitimacy to the team’s woebegone back end, and perhaps finally stabilize a group that was routinely substandard last season. It’s also about Sweeney and the Bruins pulling it off without compromising the Black and Gold’s long-term future any more than management has already done with some ill-advised moves over the past year.

That will be the tricky part as other NHL suitors queue up to start the bidding for puck-movers such as Kevin Shattenkirk and Cam Fowler. A source with knowledge of the situation told CSNNE.com on Friday morning that “there’s a very good chance [Shattenkirk] is a Bruin, Ranger or Flyer” when next season opens in October.

Of course, Shattenkirk, 27, will also be looking at a seven-year deal worth $7.5 million per season if Bruins want to hold onto the All-Star defenseman beyond 2016-17, after the Panthers signed Keith Yandle to a massive $44.5 million contract this week.

The big question for this weekend is at what cost Shattenkirk will be delivered?

Will the Bruins be pushed into giving up the 14th overall pick in the first round and potentially deal away the chance to draft Dante Fabbro or Charlie McAvoy, who could both be a Shattenkirk-level All-Star defenseman within the next three years?

“I think Fabbro is exactly the same as Shattenkirk was at this stage in his development,” said one talent evaluator for a Western Conference team. “He can move the puck, he makes decisions quickly and there’s a certain smoothness to his game that’s very similar. He’s going to be a very good defenseman in the NHL someday.”

Sources with knowledge of the situation were skeptical that the 29th overall pick in the first round would be enough, along with a young forward, to get the deal done with St. Louis for Shattenkirk. But Sweeney would also be wise to hold to that stance and fight the temptation to deal away a draft pick that will get the Bruins a good, young player ready to contribute within a couple of years.

“There are two sides to it. You have to look at what the cost may be relative to the situation that we’re in. We have two first round picks, so I’m exploring all opportunities with them. I feel very good about making two selections if that’s the direction we go because acquisitions costs are too high,” said Sweeney, who said it would have to be a “very substantial” player to get the Bruins to make the 14th overall pick. “Then we’d go back into the UFA market if needed. We’re pursuing all of it. We’re not going to stop. It’s just a matter of whether or not the line for buying into some players is too punitive to wade into.”

There’s also the problem that GMs with young, restricted free agent defensemen like Jacob Trouba will be demanding that the Bruins part with David Pastrnak or Frank Vatrano, and that’s if the Bruins aren’t already outbid with names like Matt Duchene and Taylor Hall swirling around as potentially available for trade. That’s the difficult neighborhood Sweeney is traversing through this weekend amid a gauntlet of greedy, opposing GMs and it doesn’t allow for any more flubs from the B’s front office.

“The forecasting part of the business is difficult, obviously. Whether or not you take a player [in the draft] that in two or three years will be ready, or maybe not,” said Sweeney. “I’ve used Kyle McLaren a long time ago as a guy that walked through the door [to NHL training camp] and surprised everybody. So, we get excited whether it’s Brandon Carlo, Robbie O’Gara or Matt Grzelcyk. Those are going to be good pieces for our organization, but it’s up to each individual player as to when they’re going to be ready to play.

“But it’s delicate when you look at what that player is bringing to the table in reference to trading the 14th pick overall and the impact of whether that player is going to be around and part of what we’re trying to do now, and moving forward. We want to be a competitive team that has an opportunity to win each and every year, and then certain times when the window is there then you may tip the scales [to the short term] a little bit. But until you get there [from a competitive standpoint] then I think you have to be patient. My job is to build the best hockey team that I can possibly build for this year, and for moving forward. We have to be committed to the overall process. Being a competitive team that’s in a position to be in a playoff race, and win, is the only goal we have. But I’m not going to leverage it to the point where we’re just chasing it all the time.”

It will help that the Bruins have young defensemen like Carlo, O’Gara and Grzelcyk on the way, and that Sweeney believes they can perhaps contribute at some point next season, or certainly in 2017-18 after a year of AHL development. The question is whether both Sweeney and Bruins President Cam Neely will be able to see through those players’ development arcs if the Bruins again fails to make the playoffs for a third straight season.

The Bruins GM can’t afford another miscalculation sending a third-round pick to Philadelphia for Zac Rinaldo, who might never play another game in the NHL again. He can’t take pennies on the dollar like he did last season in a rash, rushed Dougie Hamilton trade that undoubtedly has the 29 other NHL GMs feeling like they can swindle the Bruins when push comes to shove.

One thing that’s a positive for the Bruins, however: Sweeney still feels like there are multiple targets that will yield the B’s a quality NHL defenseman as soon as this weekend. With Sami Vatanen signing in Anaheim and both Alex Goligoski and Yandle signing long term deals with Arizona and Florida, one might think that the D-man supply was running a little thin.

But Sweeney is having multiple conversations with a number of teams, and even hinted that some names are in play that haven’t been widely circulated in the usual NHL rumor mills. This is where names such as Dmitry Kulikov fit into the equation if the Bruins are beaten to the punch for both Shattenkirk and Fowler.

“There’s supply everywhere. I’ve had discussions with multiple teams about players, and you might not even necessarily know that they’re available,” said Sweeney. “It’s just a matter of how it all lines up. We have targets and we have players that we think will improve our hockey club.

“There are plenty of them still available. Whether or not they land, I can’t sit here and tell you with absolute certainty that one is coming our way. But we’re in talks with several teams to see. But I’m not going to chase it because I think our younger players are going to push. But we’ll look to improve in every way, shape or form that we can.”

The Bruins have talked a great deal over the last year about improving their back end, but this weekend is the time when they need measured, prudent action more than the optimistic, hopeful words.