Docs were able to save Miller's leg ... and the 34-year-old tried to make an NFL comeback -- but he announced Tuesday he's officially callin' it a career.
"I would love more than anything to step on Soldier Field one last time but I physically cannot give the game and our fans what they deserve," Miller wrote.
"It’s difficult to find words to express my love and gratitude to every single person that has cheered my name, picked me up and stood strong with me throughout my time in this league. I am forever grateful."
Miller played 7 years in the NFL ... catching 146 passes for 1,631 yards and 15 TDs.