Greg Cook
Here’s how good Cook was: Bill Walsh, who coached Hall of Fame quarterbacks Joe Montana and Steve Young, told NFL Films that Cook “could very well have been remembered or noted as the greatest quarterback of all time.” Three games into his NFL career, he suffered a torn rotator cuff that went undiagnosed. He returned that season and led the league in quarterback rating, according to Pro Football Reference. But he’d play in just one more game, in 1973.