Bruins general manager Don Sweeney made his first real move of the offseason with Friday’s re-signing of defenseman Matt Grzelcyk to a two-year contract worth $2.8 million in total (giving Grzelcyk a $1.4 million cap hit for the next two seasons).

It’s a deserved reward for the Charlestown, Mass. native, who impressed with smart moves in all three zones, solidified the B’s bottom pairing, and contributed three goals and 15 points in a 61-game rookie season with the Bruins.

“The way [Matt] Grzelcyk came in, I was really impressed with how he played,” Bruins president Cam Neely said. “He had an element on our back end that we didn’t necessarily have as far as puck retrieval, making a good first pass.”

But this new deal has done nothing to help solve an increasingly cloudy picture surrounding Boston’s 2017-18 defense corps.

For one, the Bruins are set on their right side. With four options, no less, between Brandon Carlo, Charlie McAvoy, Adam McQuaid, and Kevan Miller. The Bruins will have no shortage of options when it comes to configuring their optimal right-side mix. On the other side, even at 41, Zdeno Chara is still the rock of Boston’s left side. That will remain the case in 2018-19.

But behind the 6-foot-9, hard minute-eating Chara, it’s Grzelcyk (with this new, highly-affordable contract) and power-play dynamo Torey Krug (under contract at $5.25 million for the next two seasons), two 5-foot-9 defenders.

This is something that the B’s were somewhat wary of from the start.

“One of the concerns I had from day one was both having Torey and Grzelcyk on the left side,” Neely admitted. “Obviously, with Zee, big body. Those two guys, a little smaller, but having said that, Torey does an extremely good job for us, especially on the power play. We’d like to see him a little bit quicker, if we can, five on five. That’s an area of improvement for Torey.”

Both truly excelled in their roles last season, though, and it seemed almost doable.

When paired together on Boston’s third pairing, the Grzelcyk-Miller duo finished with the league’s seventh-best on-ice goal differential at five-on-five, and their possession metric was the 11th-best in the league among pairings with at least 500 minutes of five-on-five play together. Krug, meanwhile, came through with 59 points in the regular season, which was the ninth-most among all NHL defensemen. The 27-year-old Krug then posted three goals and 12 points through 11 postseason games, which stood as the most among all postseason defenders when his season was ended with a fractured ankle. He’s now posted five goals and 22 points in his last 23 playoff games, and with nine goals and 28 points in 38 career playoff games.

At the same time, the 2018 postseason may have told the Bruins that supporting cast on the left is too redundant to work.

“As far as size goes, would it be nice to have a little bigger on the left side other than Zee? Yes,” Neely outright acknowledged. “So, that’s something, I think, Don was going to try and work on this offseason, but that’s not to take away from what the guys did for us that played on the left side this year. I thought they played very well for us.”

Neely has essentially outlined the left side of their defense as the fix this offseason. Sweeney, meanwhile, has openly been on the hunt for this upgrade for four offseasons now. It’s perhaps the last thing he truly needs to acquire or develop for this team to truly reopen their Stanley Cup window as a legitimate contender. The Bruins will also not carry eight defensemen regularly again next season, especially when your two scratched defensemen would account for $4.1 million of your available cap space.

Break it down simply: It seems that one of Krug and Grzelcyk gotta go.

And nothing about that decision should be easy.

At $1.4 million per year, and with impressive shot-suppression marks last season, Grzelcyk is not a player that you would be hurrying to rush out of frame. Especially when he will remain under team control at the end of that contract, too, as an arbitration-eligible restricted free agent. It’s also unlikely that the Bruins can rely on Krug, well into his career at this point, to suddenly replicate the defensive instincts and separation skills that Grzelcyk used to make himself a legit go-to this past year.

On the other hand, while it’s possible that the Bruins are just scratching the surface of Grzelcyk’s impact, is he ever going to become the offensive threat that Krug has emerged as? It seems thoroughly unlikely given his past resume and Krug’s recent.

Since signing his latest contract, Krug has been the league’s fifth-highest scoring defender. The four players above Krug and four players below Krug in terms of production in the last two seasons carry about an average cap hit of over $6 million. Often miscast as a ‘power-play specialist only,’ Krug also has more five-on-five first points (goals and primary assists) than names such as Oliver Ekman-Larsson, Mark Giordano, and Duncan Keith over that two-year sample. (Ekman-Larsson, mind you, just signed an extension for upwards of $8 million per year.) Even with his defensive-zone shortcomings, Krug’s $5.25 million per year salary is perfect for the current Cup window and in a game with an increased focus on offense and skill.

But the playoffs were eye-opening when considering the struggles Krug had when paired with Miller.

On the ice for 10 goals against, that pairing allowed the second-most goals five-on-five goals in the entire 2018 Stanley Cup Playoffs. Only the Caps’ Orlov-Niskanen pairing allowed more goals (17), but that was in 11 more games and en route to a Stanley Cup, so they had a significant minute advantage to say the least. The Krug-Miller pairing was actually tied with Nashville’s Ekholm-Subban pair and the Penguins’ Dumoulin-Letang pairing in goals allowed. But Krug-Miller were together for just 91 minutes, while Ekholm-Subban played 235 minutes together and Dumoulin-Letang played just under 180 minutes together. The Krug-Miller pairing also tied for the worst goal differential of the postseason, at minus-5.

In other words, Krug-Miller were just a woeful match together, which is not great news given the fact that that’s who he would be paired next season should the Bruins upgrade the left side of their top four while also keeping Krug in Boston.

Break their choice down even further and the B’s have to decide between an established player bringing production that they will not find on the open market for less or a more affordable player whose price and style fits a third-pairing infinitely better.

The Bruins could also do nothing and simply roll with this group on their left side for another run.

But it seems that they’ve already said — and spent — too much to go ahead with that plan.