NFL legend Gale Sayers has been diagnosed with dementia ... and his wife says football is to blame.
Ardythe Sayers told the Kansas City Star the 73-year-old Hall of Famer was diagnosed 4 years ago -- but still remains in excellent physical condition.
Ardythe says Gale has been treated at the Mayo Clinic and the doctors agree football is a factor.
"It wasn’t so much getting hit in the head," Ardythe said ... "It’s just the shaking of the brain when they took him down with the force they play the game in.