The Detroit Red Wings have assigned the forward prospect to Grand Rapids, where he'll begin the season with the Griffins.
On Monday, head coach Jeff Blashill said only one of Mantha and Andreas Athanasiou would make the opening-night roster, meaning the latter has secured his spot.
Mantha, 21, was selected with the 20th pick of the 2013 NHL Draft, and came highly touted after scoring at will during his junior-hockey days with Val-d'Or of the QMJHL.
He played 60 games for the Griffins last season, recording 21 goals and 24 assists. In 10 games with the Red Wings, Mantha has scored two goals, adding one assist.
Athanasiou was a fourth-round pick in 2012, and scored nine goals in 37 games while receiving limited ice time with Detroit last season.
We saw superstars switch sweaters and another stay put - all this in a matter of minutes. We saw a legend add to his legacy, another head back home, and a group of players on their way to achieving such status team up to redefine the meaning of fantasy hockey.
There was a lot to unpack in these last four months. But with the season now just hours away, we will have that much more to chew on. Here are five things to keep an eye on ahead of the 2016-17 season:
The P.K. Subban Show
Even before the transaction - and one of the biggest trades in NHL history - the Nashville Predators were becoming appointment viewing. With Roman Josi at the controls, and a three-headed monster in Ryan Johansen, Filip Forsberg, and James Neal on the front line, the club was emerging as one of the league's elite teams, and through highly agreeable means.
But with P.K. Subban, the defenseman with box-office appeal and whose skills jibe with their activation style, the Predators have something different. This is a player that elevates them beyond just title contender; with him they've become fashionable. With eyes now on them, it may soon be realized that the hockey in Nashville - fast-paced, uptempo, attacking - is the sort we clamor for.
For another season, Subban will be who we're talking about. Only it will be in Nashville, where his talent is encouraged, his personality magnified, and where he will be motivated to show the Montreal Canadiens just how short-sighted they were. It should be for all the right reasons.
And in Montreal
On the flip side, the Canadiens will be fitted directly under the microscope - with a mob of critics eager to pounce.
Of course, it was the Canadiens who sent Subban to Nashville in exchange for Shea Weber, the expensive veteran defender they believe better fits their style with the punishment he can dole out in the defensive end, and his tendency to get rid of the puck as quick as possible.
But there are more reasons to critique Marc Bergevin's process. He added Andrew Shaw, a player constantly straddling the line that determines what's acceptable behavior and what's not, and who, mere strides into his tenure, was sat down by the Department of Player Safety. And he also paid big money to Alexander Radulov, a talented forward whose character led to him spending the bulk of his career tearing up an inferior league rather than the NHL.
Thankfully for Montreal, potentially poor decisions can, and presumably will be masked by Carey Price. In his return from a season undermined by injury, the great neutralizer can keep Montreal formidable no matter what.
If not the Canadiens, then?
Eight points.
That's the closest a Canadian entry came to qualifying for the postseason last year, as for the first time in nearly a quarter century the country was without a franchise based within its borders in the playoffs.
It can be argued that to at least some extent, all seven teams have improved their chances. We mentioned that Montreal has its goalie, and now so do the Flames. Winnipeg has its dynamic scorer, and Toronto its franchise center, while the Oilers are piecing together a balanced roster around theirs. Vancouver has a winger for the Sedins and a better back line, and the Sens have a new coach and a power-play specialist.
And yet, eight points still seems like a heckuva lot to make up.
Just a season removed from racking up 110 points, Price's Canadiens must be considered the favorite to return - despite how fragile they may be without him. Can the rest take solace in the process?
Sid
The "What's wrong with Sid?" debate is no fun when he's on the ice. But we'll take it every day of the week if it means not having to ask the same question about his health.
In a shocking announcement just days before the season, Sidney Crosby, the Pittsburgh Penguins captain who has been pushing his performances to brand-new heights, was diagnosed with another concussion.
Of course, any head injury should be considered a serious matter. But for Sid, the ill-effects and subsequent first diagnosis in almost five years, threatens to reintroduce the health problems that have already taken a substantial chunk out of his legendary career.
It was just a few days ago we were debating if Connor McDavid could chase down Crosby, and in his teens, establish himself as the game's best player. Now we're hoping, begging, praying Crosby has even a chance to put that off for a while.
With regard to Vegas
We're closing in on exactly one year before the NHL becomes the first big four league to bring professional sports to Las Vegas, but the ramifications of that venture are already having an impact.
This season, every decision made by NHL executives must be with the upcoming expansion draft in mind. That means thorough evaluation of players from within, while assessing the risk attached with adding and subtracting bodies in pursuit of the main goal: a championship.
As a sidebar, Las Vegas does pose the greatest threat to teams with those title aspirations. Take the Penguins and Tampa Bay Lightning - the Eastern Conference finalists from last year - who each face massive decisions with regard to their goalies. Pittsburgh not only has to find a taker on Marc-Andre Fleury, but also convince the netminder himself to move on, or it will most certainly lose Matt Murray. The Lightning, meanwhile, must assess the risk of both hanging on to Ben Bishop and receiving nothing in return on a valuable asset, as well as the prospect of Andrei Vasilevskiy being able to lead them to the Stanley Cup many have them pegged to win.
The forward missed training camp due to a bout of mono, and general manager Pierre Dorion said a stint with the minor-league club will help Lazar get up to speed.
"We received some good news regarding Curtis on Monday in that he has been medically cleared to take contact," Dorion said Tuesday in a statement. "Knowing that, we then met with the coaches and player and made the decision that the best and fastest way for him to get ready to both play and succeed in the NHL is for him to go to Binghamton.
"He'll have the opportunity there to immediately play big minutes and in all situations, something that is necessary for him to get back into game shape."
Dorion added he expects Lazar to remain an important piece for Ottawa, and to rejoin the club soon.
It appears as though Tyler Seguin won't miss any regular-season action after fracturing his heel at the World Cup.
That's what Dallas Stars head coach Lindy Ruff believes, at least, saying it looks like the center will be ready for the team's season opener Thursday despite not seeing any preseason action to date.
"It's hard to describe where 100 percent is, but every day (in practice) is better," Ruff said, per Mike Heika of the Dallas News. "It's hard stepping in without game action, but leading up to (the heel injury) he had a couple of weeks of hard work with the World Cup team."
The Stars, however, will remain cautious with Seguin's progress over the next couple days, but a date with the Ducks on Thursday seems likely.
After the World Cup of Hockey and a preseason slate, the curtain on the 2016-17 NHL season rises Wednesday night at 7 p.m. ET in Ottawa, where the Senators host the Toronto Maple Leafs.
Catch up on all the details from a busy offseason and have a look at projected lineups and previews for each team, below.
Here's how the roster looks as the season opener approaches:
Forwards
LW
C
RW
Leo Komarov
Nazem Kadri
Milan Michalek
James van Reimsdyk
Tyler Bozak
Mitch Marner
Zach Hyman
Auston Matthews
William Nylander
Matt Martin
Peter Holland
Connor Brown
Matthews begins the season as the third-line center but should have no problem surpassing Bozak before long.
The Hyman-Matthews-Nylander line has looked great in the preseason, so it's not inconceivable that the unit stays together whether Matthews plays in the top or bottom six.
Defense
LD
RD
Martin Marincin
Morgan Rielly
Jake Gardiner
Roman Polak
Matt Hunwick
Nikita Zaitsev
Zaitsev joins the Leafs after spending seven seasons in the KHL. The 24-year-old played the last three campaigns with CSKA Moscow, notching 26 points in 46 regular-season games and 13 more in 20 playoff contests.
Goalies
G
Frederik Andersen
Jhonas Enroth
Andersen finally an undisputed No. 1 starter after being acquired in a trade with the Anaheim Ducks. Enroth has proven to be a capable backup who can step into the lead role if necessary.
Years of suffering and accumulating draft picks have yielded a slew of prospects, a handful of which now appear primed to make an impact.
Here are three players to keep an eye on in blue and white this season:
Auston Matthews
The centerpiece of the Leafs' plans won't need any seasoning in junior or the AHL. He's ready.
Matthews has shown he can already hold his own at the pro level - playing in the Swiss league last season - and on the international stage, impressing with the U.S. at the World Championship and starring in Team North America's short-lived World Cup appearance.
Temper your expectations for the No. 1 overall pick from June's draft, but neither a 50-point season nor a Calder Trophy nomination would be shocking.
William Nylander
Nylander has already given Leafs fans a taste of his skill, scoring six times and adding seven assists in a 22-game NHL stint last season.
The 20-year-old will have a longer stay this time around, especially if he continues clicking with Matthews and Zach Hyman on a tantalizing all-prospect line.
Nylander has all the tools to succeed at the NHL level, and the eighth overall pick in 2014 should produce plenty of highlights in 2016-17.
Mitch Marner
Matthews and Nylander might be further along in their development, but Marner isn't far behind.
The 19-year-old tore up the OHL in his final two seasons with the London Knights, posting 242 points in 120 regular-season games and taking his game to another level in the 2016 playoffs, notching 44 points in 18 postseason contests.
Setoguchi skated with Anze Kopitar and Dustin Brown at practice Monday. The 29-year-old was invited to Kings camp on a pro tryout agreement last month.
He spent last season with HC Davos in Switzerland after splitting 2014-15 with the Calgary Flames and their AHL affiliate.
Setoguchi got a tryout with the Toronto Maple Leafs last summer, but was released before the start of the season. After being invited to Leafs camp, he admitted checking into rehab just months beforehand.
