A former National Football League player from Michigan filed a lawsuit yesterday against the league and four others for failing to warn him of football-related head injuries, reports the Associated Press. Derrick Walker lives in West Bloomfield, and he began his football career playing for the University of Michigan Wolverines where he served as co-captain in the 80s. Since then, the plaintiff went on to play tight end professionally for the San Diego Chargers, the Kansas City Chiefs and the Oakland Raiders. Over that time period, Walkers lawsuit says he was concussed multiple times which led to memory loss, difficulty concentrating, headaches and difficulty sleeping. Now hes seeking at least $500,000 in damages, reports the Detroit Free Press .