Four former NFL players are suing the league over long-term injuries they say were caused by concussions they suffered as athletes.

The suits were filed Wednesday in the U.S. District Court in Atlanta on behalf of Jamal Lewis, Dorsey Levens, Fulton Kuykendall and Ryan E. Stewart.

The men, all Fulton County residents, say they suffer from memory loss, headaches and sleeplessness as a result of multiple traumatic brain injuries during their careers.

The suits allege that the NFL was negligent in its research of head injuries and concussions and downplayed the link between concussions and brain damage. The league also is accused of fraud for materially misrepresenting the risk to players, failing to warn them and not adequately protecting them.

Mike McGlamry, the lead attorney in the litigation, compared the relationship between the NFL and concussions to the relationship between tobacco companies and cigarettes.

“The NFL didn’t want to find a significant problem (with concussions) because of how damaging it would be to their product,” he told the AJC.

Lewis, 32, a former running back for the Baltimore Ravens and Cleveland Browns, concluded a 10-season career in 2009. The 10,000-yard rusher was born in Atlanta and attended Douglass High.

Levens, 41, also a former running back, played 11 seasons, ending in 2003. He had stints with the Green Bay Packers, Philadelphia Eagles and New York Giants after attending Georgia Tech.

Former Falcons linebacker Kuykendall, 58, played with Atlanta from 1975 to ‘84 and spent the 1985 season with the San Francisco 49ers.

Stewart, 38, played five seasons at safety for the Detroit Lions after his collegiate career at Georgia Tech. He is currently one half of the “Two Live Stews” sports talk radio team on Atlanta’s 790 the Zone.

All of the former players are demanding a jury trial and seeking payment for medical expenses, past and future loss of earnings, general damages for pain and suffering, punitive damages and attorneys’ fees.

The Atlanta firm Pope, McGlamry, Kilpatrick, Morrison & Norwood represents the former players.

The AJC is attempting to contact the NFL for a response.

The league announced Wednesday that it is changing its concussion protocols after Cleveland Browns quarterback Colt McCoy returned to a game after a helmet-to-helmet hit Dec. 8 without being examined for one. McCoy, who was diagnosed with a concussion after the game, is still experiencing symptoms and hasn’t played since.

A league-paid, certified athletic trainer will be at each game to monitor play and assist medical staffs, though trainers can’t order that players be removed from a game.

“The players know the game is violent and dangerous, but they don’t really know what that means for them long-term,” McGlamry told the AJC when discussing the lawsuits.

He said the pressure is on players to go back into the game after getting hit.

“If the league says you’re OK, what are you supposed to think?” he said.

Please return for updates.

–The Associated Press contributed to this article.