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.
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.