The former NFL star said smoking weed was necessary to cope with pain. Johnson also admitted that the NFL had an opioid problem in a recent interview with 'Sports Illustrated.' Calvin Johnson, via 'Sports Illustrated' Calvin Johnson, via 'Sports Illustrated' The former wide receiver estimated that he suffered "at least nine concussions" during his football career. Johnson had multiple injuries throughout his career, including lower-back issues and ankle and knee injuries. Johnson unexpectedly retired from the NFL in 2016 after a nine-year career with the Detroit Lions.