Former Detroit Lions star receiver Calvin Johnson retired from the NFL following the 2015 season, and even if he wanted to return to the league, he doesn't believe he could do so.

"I don't [think so], man, cause I get up from the bed sometimes in the morning, I'm just like, I shuffle across the ground cause I can't bend my ankles," he told Dave Birkett of the Detroit Free Press. "That was my problem when I played, just ankles always stuck or swelled up; I can't flex them. If you can't flex your ankles, then you're just running flat-footed all the time."

Johnson also said he may donate his brain to science for CTE research once he dies, though he noted he doesn't suffer effects from concussions.

Johnson, 32, was one of the NFL's most dynamic weapons and talented wideouts during his nine-year career. He was voted to six Pro Bowls and was a three-time All-Pro. He caught 731 passes for 11,619 yards and 83 touchdowns, registering seven seasons with more than 1,000 receiving yards and four seasons with at least 12 touchdowns.

His retirement came as a surprise to many people, as he was in the prime of his career, though Johnson told Birkett he had to be convinced to even play his ninth and final season.

"I told [my father], I was like, 'Dad, I don't think I can do it no more,'" Johnson recounted of the offseason before the 2015 campaign. "I was like, 'I don't think I can keep on coming out there running miles a day.' He said, he was like, 'You think you can get one more?' I thought about it. ... I was like, 'All right, I can do it one more time.'"

Johnson said he felt relieved after he told then-Lions head coach Jim Caldwell at his exit interview of his retirement plans.

"It was actually tough to actually say it, to spit the words out," Johnson said. "But when I finally told him, it was like a burden off my chest like no other. I was like, 'Man, I'm free. I ain't got to be stressing this [stuff] no more.'"

He's stayed busy in retirement as a father and husband and runs a consulting business, Locker Room Consulting, with former Lions offensive lineman Rob Sims and former Michigan State offensive lineman Jason Strayhorn. He also has consulted as a wide receivers coach and is involved in real estate.

"[Retirement] takes you down a path in life that you have unsurety about how to deal with certain things," Johnson said. "It's like you're starting all over on how to be successful. You got to go through some bumps and bruises, some learning experiences to kind of work your way to the top."

As for the Hall of Fame, Johnson will be eligible in 2021 and will certainly make a compelling case. While his career numbers aren't among the leaders' at his position—he's 22nd in touchdown receptions and 29th in yards—he was an elite receiver in his playing days.

Regardless, the man nicknamed Megatron isn't overly worried about Canton.

"People don't like that I didn't play a long time, but hey, it is what it is," he said. "I mean, I was the fastest to 10,000 yards, I had the most yards [329 on Oct. 27, 2013, against the Dallas Cowboys] in an actual regulation game. I did some things, but if it's not enough, it's not enough. I'm not going to lose sleep over it."