Shiny as a new penny, his full asset value yet unknown, Charlie McAvoy was promoted to the Bruins’ top defensive pairing Tuesday, only one day after signing his first NHL contract, and only one day prior to Boston taking on Ottawa in Game 1 of the postseason.

McAvoy, who only two weeks ago was a Boston University sophomore, eyeing burgers and the pizza-of-the-day selection at the Comm. Ave. student union, was paired in practice with future Hall of Famer Zdeno Chara. He also manned (or is it “wunderkinded?’’) the right point on the first-unit power play.

Until further notice then, the 19-year-old McAvoy, with all of 0:00 NHL career ice time, stands as a key factor in whether the Bruins, in their first postseason appearance since 2014, will take a first step toward the 16 victories they need to clinch the Stanley Cup.

“It’s just about realizing where you are, taking it all in,’’ mused McAvoy, accustomed to big stages, including Beanpot play, World Junior action, and NCAA playoffs. “Not missing a beat of it, but showing up and realizing this is something I’ve wanted for a long time.’’

McAvoy might not have been offered a Boston contract had it not been for mounting injuries on the back line, specifically the losses last week of Torey Krug (knee) and Brandon Carlo (either concussion or shoulder injury). But with those two key contributors hors de combat (return dates uncertain), the Bruins’ first-round pick from last June was hustled here from AHL Providence and signed.

The Bruins were willing to surrender a year of salary control in hopes that McAvoy can 1.) Stop the bleeding on the back line and 2.) Perhaps replace, or even enhance, the offensive element lost when Krug was hobbled.

For his part, coach Bruce Cassidy was not ready to offer a full-throated buy-in on McAvoy as Chara’s partner in Game 1. Asked after practice what reluctance he would have in pairing the two, Cassidy said, “There’s not a lot till I see him play.

“My reluctance with Charlie, or whatever matchup, is, ‘Let’s see him play. How does he handle defending? What matchup best suits him?’

“And without seeing him play live at this level, it is a bit of guesswork. We can’t assume how he’s going to be. And they have never played together, I guess, would be the second part.’’

Cassidy quickly added the obvious: With McAvoy on board for only two practices thus far, the coach hasn’t seen him play with anyone.

“Z’s at least played with [Adam] McQuaid,’’ noted Cassidy. “Even Colin Miller, if we moved him up, [Chara] played with him last year. I think ‘reluctance’ is not the best choice of words. In this case, I think just ‘uncertainty’ would be a better word, for me, anyway.’’

Adding to Cassidy’s losses, the Bruins on Tuesday also were without two of their key forwards, No. 2 center David Krejci and fourth-line stalwart Dominic Moore. Both needed time off the ice for “maintenance,’’ said Cassidy, noting that he remains hopeful both will be able to suit up for Game 1 Wednesday in Ottawa.

Meanwhile, man-child McAvoy also slipped into Krug’s spot, right point, on the No. 1 power-play unit, with David Pastrnak at the left point. The look perhaps foreshadowed the moment when the Bruins will have two point men on their top man-advantage unit without one minute of postseason experience.

“Charlie seems very skilled,’’ said a beaming Pastrnak. “I don’t think it will be a problem.’’

Up front, the power-play unit remained the same, with Patrice Bergeron flanked by Brad Marchand and Ryan Spooner. The No. 2 unit, absent Krejci, had David Backes with Drew Stafford and Matt Beleskey up front, backed by Chara and John-Michael Liles.

McAvoy looked fluid and composed at the point, be it dishing passes for Pastrnak to tee up, or shuttling it down the right wall for the clever Spooner to dish into the middle. Based on the overall workout, it’s all but a certainty that Cassidy will go into Game 1 with McAvoy slotted to handle the workload of, say, a five-year vet. He’ll give the kid a chance, then adjust if necessary.

“I think he is a player we have to see in a game to truly evaluate,’’ said Cassidy. “We put him on the power play, to try to evaluate his composure level out there. Even though it’s only a practice . . . what he sees, you know, he looked good. He moved the puck well.’’

At his best with the Terriers, Mc-Avoy was a proficient puck-mover, which is why the Bruins were enticed to use their No. 14 pick in last year’s draft to land him. He can move, he can skate with the puck, deliver it to the forward group with clean passes, and also land a smack or two when the chance arises. Those are rare attributes. Now it looks as though he’ll have the rarest opportunity to display them all, in the heat of the playoffs.

“I’m kind of playing off the experience I had in Providence,’’ said McAvoy, who tuned up with the AHL Bruins for four games prior to signing in Boston. “Some guys are stronger and faster, for sure. Guys are hard on their sticks. You don’t have as much time with the puck, and plays are harder to make.

“But at the same time, I just have to play my game. I was able to have some success in Providence, moving the puck and moving my feet. Here, I am playing with so many great players, if I can just get the puck in their hands, play a simple game, get the puck in their hands — that’s what I’ll try to do.’’

Follow Kevin Paul Dupont on Twitter at @GlobeKPD.