The Toronto Maple Leafs have not been dressing their best six defencemen and we’re not just talking about the injured Jake Muzzin here.

As head coach Sheldon Keefe experiments with defender Martin Marincin — who signed a one-year extension Friday — in his top four against Connor McDavid and challenges/rewards Travis Dermott with tough minutes head-to-head versus a three-headed monster like Kyle Connor–Mark Scheifele–Patrik Laine, the club has kept an intriguing wild card in the pocket.

Rasmus Sandin, 19, may be young — at least according to his birth certificate — and he is certainly benefitting from the extra minutes and seasoning that comes with his current big-fish-in-a-small-pond status, but his farm-system performance is beginning to scream for a call-up to the real squad.

Sandin’s confidence and his game is arguably at its highest. His standout performance in the world juniors’ bronze medal game led Sweden to bronze. His 3-7-10 stat line in the tournament’s seven contests bested all blueliners and secured him Top Defenceman honours in Ostrava. He was recently named to the AHL all-star game.

There is a swelling momentum here begging for a promotion, and the Leafs are only carrying six D-men.

"Obviously, he’s an important player for our future, but we feel like we’ve been going pretty well here as a group, even without Muzzin," Keefe said this week. "But we recognize, whether it’s [Timothy] Liljegren or Sandin, that both guys are right there, and they’re playing lots and they’re part of things with us and keeping an eye on what’s happening.

"We know they’re only a call away if we need to make a change or add somebody."

The Maple Leafs have gone a respectable 3-1-2 since a P.K. Subban point blast fractured Muzzin’s foot.

Aside from Monday’s loss to the Oilers, the result of a weak overall effort, Twitter’s whipping boy, Marincin, has held his own.

Despite being a minus on the Wednesday, Dermott looked inspired by the challenge of shutting down Winnipeg’s top unit and was a physical presence.

"Part of that is just to try to get Derms to take that next step at this phase in the season, and we think he’s an important guy for us to be able to get a little bit more from him," Keefe explained.

Now 45 games deep, the Leafs don’t truly have a handle on the optimal six-man combination on the blue line. Part of that is a coaching refresh and Keefe’s openness to experimentation. Part of that is injuries.

"You get guys in there, you give guys more responsibility, and you expect guys to take that and run with it," says Morgan Rielly, the club’s top minutes muncher. "If you look back at wins and losses since [Muzzin] has been out, I think we’ve done a pretty good job. That being said, there’s always areas for improvement."

The other part of that is Sandin, sharpening his skills and his teeth in the shadows since being sent down to the American League by Kyle Dubas after the six-game mark of the season.

"Up with the Leafs, I was averaging about 13 minutes or so a game. Down here, I am probably playing double," Sandin told Good Show Wednesday. "When you get confidence as a hockey player, that is how you build your game.

"I know it is not easy to crack a roster when you are 19 years old as well, but that was one of my big goals this year — to crack the lineup — and I did. After that, I was just trying to play as well as I could every game and every practice to stick around. Obviously, you are going to be disappointed when you are getting sent down, but you’ve got to see the good things about it."

Keefe, who’s worked closely with Sandin for a year and a half, sees the kid’s dominance at the world juniors as another positive step in his accelerating development. He’s already seen it firsthand with William Nylander, Kasperi Kapanen and Liljegren.

"It is the chance to play with their peers and represent their country and play in a high-pressured environment," Keefe said. "It’s just a really good step for a high-end young player, and one that services players really well going forward."

Going forward, Dubas faces a compelling decision: How much of the future do you sacrifice for the now? And how many standings points does swapping Marincin for Sandin really get you?

On a personal-growth level, it seldom does a teenager harm to spend a few more months dominating a league that may be a notch lower than what they’re worthy of.

And there is a great argument to be made that a club as cap crunched as the Leafs must resist the temptation to play Sandin four more NHL games (10 total) and permit his entry-level contract to slide till 2020-21.

Sportsnet’s Brian Burke, an experienced exec, believes it foolish not to use the CBA to your advantage in a situation like this, arguing that Dubas will need cheap talent like Sandin for the three seasons after this one. He’s not wrong.

On the flip side, Tampa is charging fast, catching the Bruins is a possibility, and home ice in the postseason sure would be a pleasant change.

Can that be accomplished when an already-thin blue line isn’t being represented by the best six talents in the organization?