Injuries were a major story in the NHL last week with Ottawa Senators superstar defenseman Erik Karlsson suffering a season-ending injury.
The Senators, and many other teams, have been forced to give unproven young players larger roles this season while star players are out of the lineup because of injuries.
Let's take an updated look at the most notable injuries in the NHL heading into Week 5 of the 2013 season.
Erik Karlsson, Ottawa Senators
The Senators' chances of making the playoffs took a major hit last week when the team learned that its best player and reigning Norris Trophy winner would miss several months with an Achilles injury.
The incident between Karlsson and Pittsburgh Penguins forward Matt Cooke that led to the injury has sparked a lot of discussion about protective socks players can choose to wear that have the ability to prevent injuries such as Achilles tears.
After this injury, we could see a lot more NHLers consider using these kinds of socks because Achilles injuries are painful and require a lengthy recovery. At some point in the future, these types of socks could become mandatory by certain teams.
Following Karlsson's injury, don't expect Ottawa to ruin its rebuild by trading quality draft picks and prospects to compete for a playoff spot this season, because the Senators are a young team with a bright future ahead of them.
Scott Hartnell, Philadelphia Flyers
According to Sarah Baicker of CSN Philadelphia, Scott Hartnell is back on the ice, but there is no set date for his return to real NHL action.
The Philadelphia Flyers are struggling without their top goal scorer this season, evidenced by the fact that the team ranks 24th in goals scored and its power play is struggling. However, the Flyers offense was spectacular on Monday with seven goals in a shutout victory over the New York Islanders.
Philadelphia is only three points out of a playoff spot, so there is no reason for the team to panic even though Hartnell is unable to rejoin the lineup. This team is capable of scoring enough goals to win games against any opponent while he works his way back from injury.
Milan Michalek, Ottawa Senators
The Ottawa Senators will need Milan Michalek to step up and produce offensively with Jason Spezza and Karlsson out of the lineup, but the veteran forward is currently dealing with some injury issues of his own.
Ian Mendes of Sportsnet has the latest update:
Michalek has missed the Senators' last two games and the team lost both matchups. The 28-year-old veteran has two goals and six assists in 13 games this season, and he led the team with 35 goals last year.
If Michalek is out for an extended period of time, a large majority of the team's scoring burden will fall on the shoulders of two young forwards, Kyle Turris and 19-year-old rookie Mika Zibanejad. That's a lot of responsibility for two inexperienced players, but the Senators don't have a choice when their three best offensive players are injured.
Jeff Skinner, Carolina Hurricanes
Carolina Hurricanes star Jeff Skinner won't be in the lineup on Monday, according to Chip Alexander of the Raleigh News and Observer.
The injury doesn't appear to be anything serious, but given Skinner's importance to the present and future success of the franchise, the Hurricanes would be wise to not rush him back to game action.
The 20-year-old winger has scored seven goals with seven assists in 13 games, and his 14 points rank second on the team behind Eric Staal's 17. Skinner has also been one of Carolina's most consistent players this season with points in 10 of the 13 games he has played.
David Booth, Vancouver Canucks
Injured superstar Ryan Kesler returned to the lineup last week following his recovery from shoulder surgery, and the Vancouver Canucks could have another top-six forward available in the near future, reports Elliott Pap of the Vancouver Sun.
Vancouver begins a four-game road trip on Tuesday with games against the Chicago Blackhawks, Nashville Predators, Dallas Stars and Detroit Red Wings.
David Booth has not played for the Canucks this season, but he scored 16 goals with 13 assists in 56 games for Vancouver last season after arriving to the team via a midseason trade with the Florida Panthers.
He will give the Canucks some more size and scoring for the team's second or third line, and should also play a role in the team's power play. If he plays well in his return from injury, Booth will make an already dangerous Vancouver offense (ranked 11th in goals scored) even more difficult for opposing teams to defend.
Brendan Gallagher, Montreal Canadiens
Canadiens rookie forward Brendan Gallagher has exceeded expectations this season with five goals and three assists in the first 13 games of his NHL career, but the 20-year-old right-winger has suffered a head injury, according to Louis-André of TVA Sports.
Gallagher ranks second on the Canadiens with five goals, and his absence from the lineup would put more pressure on top-six forward Erik Cole to produce offensively.
Cole has just two goals and two assists through 14 games after scoring a career-high 35 goals last season.
Montreal is second in the Northeast Division with 19 points, but injuries to key forwards such as Max Pacioretty, Colby Armstrong and now Gallagher will test the team's depth and force head coach Michel Therrien to redo his lines to find the most effective combinations.
Tobias Enstrom, Winnipeg Jets
The Winnipeg Jets will need a strong effort from their blue line while offensive defenseman Tobias Enstrom is out of the lineup.
Chris Nichols of Sportsnet has the latest update on the 28-year-old star:
The severity of Enstrom's injury is not known at this time, but Winnipeg is 25th in goals against and has the worst penalty kill in the NHL, so losing a key member of the blue line is a major setback for this team.
Enstrom also ranks second in the league in points among defensemen, so his absence from the lineup will also have a major impact offensively.
Winnipeg is currently at the bottom of the Eastern Conference standings with the Washington Capitals (11 points each), so this is a very critical time for the team. If they don't improve, expect the Jets to become sellers near the trade deadline in early April.
Nicholas Goss is an NHL Lead Writer at Bleacher Report. Follow him on Twitter. He was also a credentialed reporter at the 2011 Stanley Cup Final and 2012 NHL playoffs in Boston.