(CNN) -- It's the issue within U.S. sport which simply refuses go away -- concussion and the potential danger it poses to professional athletes playing contact sports.
Earlier this year the National Football League (NFL) reached a settlement with thousands of former football players to pay $765 million to fund medical exams, concussion-related compensation, medical research for the retired players and their families, and litigation expenses.
Now the National Hockey League is facing a class-action lawsuit brought by 10 former NHL players.
The lawsuit says the league hasn't done enough to protect players from concussions in a sport where physical contact is common and often spills over into heated argument.
The players' legal action drew a swift response from the NHL.
"While the subject matter is very serious, we are completely satisfied with the responsible manner in which the League and the Players' Association have managed player safety over time, including with respect to head injuries and concussions," said the NHL statement.
"We intend to defend the case vigorously and have no further comment at this time."
Former NHL All-Star Gary Leema is one of the 10 players to have taken the action against the league and its board of governors.
"Unbeknownst to plaintiffs, scientific evidence has linked brain injuries to long-term neurological problems for decades," read the lawsuit, filed in a Washington D.C. court.
"While every blow to the head is dangerous, plaintiffs did not know, and were not told by the NHL, how dangerous this repeated brain trauma is.
"The NHL has known or should have known of this growing body of scientific evidence and its compelling conclusion that hockey players who sustain repetitive concussive events, sub-concussive events and/or brain injuries are at significantly greater risk of neuro-cognitive illness and disabilities both during their hockey careers and later in life."
The players claim a series of updates to the rules made in 2004, while creating a more exciting, marketable game, increased the number of violent in-game collisions.
"Hopefully this lawsuit will shine a light on the problem and the players can get the help they deserve," Rick Vaive, a former Toronto Maple Leafs player and one of 10 players who have launched the lawsuit, said in a statement.
The lawsuit also accuses the NHL of waiting until 2010 to prohibit targeting a player's head during a challenge, while also failing to outlaw body-checking.
"We have, on our own, a long history, going back to 1997, of taking concussions very seriously," NHL commissioner Gary Bettman said earlier this year.
"We spend a lot of time, money and effort working with the players' association on player safety."
The NFL agreement, which involves more than 4,500 plaintiffs, still needs to be approved by the judge assigned to the case.
Meanwhile it was announced Tuesday that Rogers Communications has paid a record-breaking $5.2 billion for the rights to broadcast the NHL in Canada.
The deal, which also includes multimedia rights, will last 12 years and is the largest in NHL history.