One of the best things a hockey team can have is depth.
That's not only because it gives coaches a chance to mix and match lines and tinker with matchups, but having talent up and down the lineup also allows clubs to move players up a slot and not miss a beat.
However, there aren't many clubs that have outstanding depth in a 31-team, salary-cap league.
What the NHL does have is a handful of players who simply cannot be replaced -- the type of player whose performance ultimately determines the team's fate, whether he is a star scorer, minutes-eating defensemen or linchpin role player.
Let's have a look at the NHL's 10 most irreplaceable stars, as well as five under-the-radar skaters whose teams would struggle mightily to replace them, even for a short period of time.
Our qualifications for the list: The player's team must rely heavily on him for production or tough defensive matchups and be short on the star power or depth to slide someone into his spot and keep going. For example, Sidney Crosby does not qualify because the Penguins could keep winning with Evgeni Malkin, and the Maple Leafs would survive without Auston Matthews. Also, we're not including goalies here, since most teams would be sunk if the starter got hurt for any extended stretch of time.
Note: All stats via Natural Stat Trick and current as of Oct. 18.
Connor McDavid, C, Edmonton Oilers
Key stat: Plus-17.9 percent relative goals for percentage (5-on-5) since start of 2017-18 season
To start his career, the best player in the world has been saddled with an underwhelming supporting cast, largely because of ill-advised trades and bad contracts. Despite a league-leading 108 points from McDavid last season, the Oilers finished with just 78 points in the standings. They are trending in the same direction early this season, with four goals and five assists coming from McDavid but only two wins in four games. So long as the Oilers get solid goaltending, their blazing-fast center is capable of carrying them into the postseason, as he did in the 2016-17 campaign. But if Edmonton lost him for any length of time, they would have excellent odds in the draft lottery yet again.
Nathan MacKinnon, C, Colorado Avalanche
Key stat: 46 goals since start of 2017-18; next best on Avs roster has 30
After three so-so seasons, MacKinnon finally returned to the form that Avs fans expected when he posted 63 points and dominated an opening-round playoff series in his rookie season. The No. 1 overall pick from 2013 broke out with 97 points and a remarkable 12 game-winning goals while maintaining his exceptional puck possession numbers (plus-3.5 percent relative Corsi for percentage). MacKinnon's ability to not only dominate the puck by himself but make everyone around him better was on display in the performance of winger Gabriel Landeskog, who managed an outstanding 66.3 percent goals for percentage while playing with MacKinnon and a mere 36.7 percent without his most common linemate. Colorado is a budding team that could soon be deep enough to hang tight over a stretch without their star. For now, however, it remains a one-line team that relies heavily on its superstar.
Tyler Seguin, C, Dallas Stars
Key stat: Stars score 1.37 more goals per 60 minutes with Seguin on ice since start of 2017-18
The Stars gave their top center a boost by signing Alexander Radulov prior to last season, and Jamie Benn certainly has helped the former Bruin rise to stardom in Dallas; but it's clear that Seguin's outrageous offensive talent has helped maximize their scoring potential. Radulov's Corsi for percentage is 5.0 percentage points lower and his goals for percentage is 9.3 percentage points lower in 500 minutes without Seguin than in the 799 minutes with him. Dallas is another team that severely lacks scoring depth. So far this season, it has only two goals by forwards not named Seguin, Benn or Radulov.
Taylor Hall, LW, New Jersey Devils
Key stat: 97 points since start of 2017-18; next best on Devils has 52
The Devils' Adam Larsson-for-Taylor Hall trade appears to have changed the trajectory of the franchise. Not only did New Jersey get a centerpiece forward in Hall, they were able to accelerate the development of 2017 No. 1 overall pick Nico Hischier by pairing him with one of the planet's most gifted offensive players. Hischier has scored 14 goals and 17 assists at even strength over 851 minutes with Hall in his early career. In the first four games of this season, the Devils have shown signs of being a legitimate contender despite Hall being held without a goal, but they do not have another player on the roster who has scored more than 30 goals at any point during his career. Hall will need to put together another Hart Trophy-caliber season in order for New Jersey to rise to the top of the Metropolitan Division.
Filip Forsberg, LW, Nashville Predators
Key stat: Preds score 1.45 more goals per 60 minutes with Forsberg on ice since start of 2017-18
Nashville has a complete roster worthy of a return trip to the Stanley Cup Final. Whether the Predators fulfill their potential will largely rest on the shoulders of Forsberg. Last season, the former Washington Capitals prospect grew from an up-and-comer to a legit superstar with 64 points in 67 regular season games, as well as 16 more points in 13 playoff games. Since the beginning of last season, the Predators have outscored opponents 60-31 with Forsberg on the ice. Nashville's exceptional blue line and improved depth forwards might be able to do enough to keep the Preds afloat, but in an extremely challenging division, they would be at risk of sliding down the standings without Forsberg.
Anze Kopitar, C, Los Angeles Kings
Key stat: Second most even-strength minutes played (behind McDavid) since start of 2017-18
The Kings are a shadow of what they were just a few years ago, but Kopitar and also-featured Drew Doughty (and goaltender Jonathan Quick) somehow willed them into the playoffs last season. At age 30, Kopitar took his offensive game to another level by scoring a career high 92 points while still handling the toughest matchups the Western Conference has to offer and also dominating the defensive side of the ice. Since the beginning of 2017-18, Kopitar has played 250 minutes more than the next most used Kings forward. Nothing quite demonstrates his ability to raise the play of others as much as winger Dustin Brown's 53.9 Corsi for percentage with Kopitar and 46.7 percent without.
Mathew Barzal, C, New York Islanders
Key stat: Islanders post 7.8 more shots per 60 with Barzal on ice
Impressively, the Islanders' young offensive dynamo led the team in scoring last season by one point over John Tavares despite 22 minutes at 5-on-5 with Tavares during his entire rookie season. Now JT is skating for the Toronto Maple Leafs, leaving Barzal to handle the load -- and face the toughest opponents -- for the Isles. You could argue that Barzal has help in the form of a 40-goal scorer and 71-point producer in Anders Lee and Josh Bailey, respectively; but it's unlikely they will be able to repeat those performances without their former linemate Tavares. Now it's up to Barzal to continue his offensive dominance and find a way to help the Isles improve their defensive play in order to give them any chance to return to the postseason.
Drew Doughty, D, Los Angeles Kings
Key stat: Most even-strength minutes played of anyone in the NHL since the start of 2017-18
Considering the Kings' lack of depth, it is remarkable that they made the playoffs last season. Doughty's ability to play outrageous amounts of minutes gives them a chance to make it again this season. Since the beginning of 2017-18, he has played more than 1,700 minutes, controlled the shot counter to the tune of a 52.5 Corsi for percentage and been on the ice for 78 goals for (third most of any defenseman) and 63 goals against. While Doughty has some help in the form of Jake Muzzin, the Kings' defense would collapse without its horse.
Mark Giordano, D, Calgary Flames
Key stat: No. 1 in relative Corsi (plus-7.0) in the NHL since start of 2017-18
No matter who Giordano has played with, he has made them better. In fact in every season since 2013-14, the veteran defenseman has had a positive relative Corsi. And since the start of last season, he ranks No. 1 in the league in relative Corsi. The Flames have dynamic forwards in Sean Monahan and Johnny Gaudreau, but they can't operate without strong breakout plays from Giordano. Calgary is not void of other blue-line talent, with T.J. Brodie, Noah Hanifin and Travis Hamonic, but none of them has proved capable of carrying the load. The Flames have playoff aspirations, but simply put, they won't get there without Giordano playing at his usual high level.
Matt Dumba, D, Minnesota Wild
Key stat: Sixth in even-strength minutes, No. 2 in NHL in relative goals for per 60 minutes among 1,000-minute defensemen
Since Ryan Suter and Jared Spurgeon are quality defensemen, this one might come as a surprise -- until you look closer at Dumba's ability to drive the Wild's offense. Since the start of last season, only one player has increased his team's goals for total more per 60 minutes at even strength than Dumba. Only Tampa Bay's Victor Hedman has more individual even-strength goals than the No. 7 overall pick from 2012, and his goals for percentage ranks 13th in the NHL in that time span. If you think Dumba is pumping up his stats because of protected minutes, well, that simply isn't the case. The lines he has faced most since the start of last season are centered by Tyler Seguin, Ryan Johansen, Jonathan Toews and Connor McDavid. If the flawed Wild have any chance of competing, it will be because Dumba continues his excellent play.
Under-the-radar linchpins
Alex DeBrincat, RW, Chicago Blackhawks
Key stat: Jonathan Toews has a 64.5 percent goals for percentage with DeBrincat, 47.1 percent without him since the start of 2017-18
The undersized winger has been partly responsible for Toews' offensive surge to start the season; the captain has nine points in five games, and DeBrincat has been involved in five of those points. His natural scoring gifts play well with Toews' ability to dominate the puck. Chicago's top center would still be good without DeBrincat, but it appears they have found something special together. The Blackhawks' lack of depth would cause them to collapse without scoring from their top players.
Sebastian Aho, RW, Carolina Hurricanes
Key stat: 77 points in 85 games since start of 2017-18
Learn the name. The 21-year-old Finnish forward has been one of the best players in the NHL to start the season, with 12 points in seven games, a plus-12 rating and a 57.7 Corsi for percentage. Last season's production indicates he can keep this up. Carolina might finally be turning the corner, with Aho as the engine.
Joonas Donskoi, RW, San Jose Sharks
Key stat: Plus-9.4 percent relative Corsi, plus-14.5 percent relative goals for percentage since start of 2017-18
Donskoi isn't exactly the biggest name in San Jose -- and make no mistake, the Sharks could compete without him -- but the solid winger provides a versatile piece that San Jose will need down the stretch, as the Sharks largely rely on stars for production. He proved during the 2016 Stanley Cup playoffs that he can step up at the right time, and the Sharks will need that if they are going to defeat the West's best.
Josh Manson, D, Anaheim Ducks
Key stat: Plus-1.08 relative goals for per 60 at 5-on-5 since start of 2017-18
Who would have guessed that Manson was the defenseman on the ice for the biggest raise in his team's offensive production? Take away power-play points and it becomes more clear that he is an offensive threat. Of his 37 points in 2017-18, 36 came at even strength.
Charlie McAvoy, D, Boston Bruins
Key stat: Zdeno Chara's 54.8 Corsi for percentage with McAvoy, 50.1 percent without
Boston will be competitive without any one player, but McAvoy controls the keys to Chara sustaining his strong play into his 40s. They are a perfect mix of net protection and toughness, along with skill and puck-carrying ability. McAvoy's skill with the puck and gift for passing perfectly complement Chara.