Gale Sayers -- who's battling dementia and is struggling daily to remember who he is -- showed up to the Bears100 celebration on Friday ... and got an ovation from the crowd that brought a tear to his eye.
The 76-year-old legend is struggling in his fight with dementia ... his wife, Ardie Sayers, says the former RB is having hard time speaking and moving.
In fact, she tells The Athletic he can't even sign autographs anymore because he can't write ... saying, "It's kind of sad because he used to love to write his name.