(ABC News) -- More than 2,000 former NFL players plan to file a lawsuit Thursday morning in Philadelphia, accusing the league of concealing information linking football-related injuries to long-term brain damage.
In the biggest sports lawsuit ever, the former players allege that the "NFL exacerbated the health risk by promoting the game's violence" and "deliberately and fraudulently" misled players about the link between concussions and long-term brain injuries.
The NFL denies the claims, saying, "Any allegation that the NFL intentionally sought to mislead players has no merit."
But with some of the sport's household names now revealing the human price paid for all those on-field heroics, this lawsuit could change football forever.
"It's America's favorite sport and its favorite athletes and now we're hearing about the dark side," USA Today sports columnist Christine Brennan said. "It really hits like a ton of bricks."
Kevin Turner, a running back for the Philadelphia Eagles until he retired in 1999, is one of the plaintiffs who can remember two documented concussions during his career. He believes he suffered long-term brain damage from his years plunging into the line. Turner, 42, has been diagnosed with Lou Gehrig's disease.
Concussions have become football's number one issue with the sport's biggest names suspected of killing themselves because of brain damage.
Former San Diego Chargers linebacker Junior Seau was found dead in his home in May after an apparent suicide. Retirees Dave Duerson of the Chicago Bears and Ray Easterling of the Atlanta Falcons are also among the suicides that have raised questions about football's unbridled violence.
Duerson, 50, shot himself last year in the chest and requested his brain be used for research.
It is estimated that two football players running full speed at 20 miles per hour can generate 1,800 pounds of force in a head-on collision.
In an attempt to protect the players, the NFL formed the Head, Neck and Spine Committee in 2010. It replaced the Mild Traumatic Brain Injury Committee, formed in 1994. Commissioner Roger Goodell also instated new rules in 2010 to protect players from direct hits to the head. Stiffer penalties and suspensions have been handed out to players who break the rules.
"Will our love of football really last," columnist Brennan said, "or will we be so horrified by the turn of events that we might find the nation gravitating away from the NFL.