Calvin Johnson: Concussions played role in retirement
Report: Calvin Johnson Drawing Trade Interest, Lions 'Willing To Listen' - CBS Detroit
Remembering Calvin Johnson's Insane 2007 NFL Combine
Calvin Johnson says retirement would've been hard if Lions were contenders
Calvin Johnson: I wanted to play elsewhere, Lions wouldn't let me : r/nfl
Lions' Calvin Johnson Reveals Origin of Megatron Nickname
Dear Calvin Johnson: Charles Tillman's Open Letter to Megatron : r/nfl
Calvin Johnson's Lions relationship 'trending up' after acrimonious split
Why did Calvin Johnson retire?
Calvin Johnson: Lions asked me to change my story about 2012 concussion - Sports Illustrated