This NFL season has seen a handful of retirements with Peyton Manning announcing the end of his 18-year career during a press conference on Monday. The sports world has not recovered from that news but another NFL great has announced that his hanging up his boots for good.

Detroit Lions wide receiver Calvin Johnson released an official statement on Tuesday, announcing that he is formally retiring from professional football. Johnson's retirement has been rumored for the past few months, but it is still shocking to learn that "Megatron" will leave the game at just 30 years old.

"After much prayer, thought and discussion with loved ones, I have made the difficult decision to retire from the Lions and pro football. I have played my last game of football," Johnson said. He apologized for announcing his retirement via a statement but expressed his gratitude towards everyone who has been part of his nine-year career.

He thanked his family, teammates, coaches, team owner, fans, the city of Detroit and state of Michigan. "From the bottom of my heart I thank you all for everything," Johnson said. "Megatron" joins several NFL stars who retired too early.

Jim Brown

The Cleveland Browns' running back is arguably one of the greatest football players of all time. Brown retired at the age 29 after only nine full seasons. He was an eight-time Pro Bowler, an eight-time All-Pro, one-time NFL champion and holder of 20 NFL records at the time of his retirement.

Marshawn Lynch

A recent retiree, "Beast Mode" announced his retirement on Twitter during Super Bowl 50. The 29-year-old running back was one of the best football players when he literally hung up his boots. He helped the Seattle Seahawks win the Super Bowl last 2013.

Barry Sanders

Just like Johnson, Sanders spent his entire career with the Detroit Lions as a running back. He played 10 seasons in the Motor City from 1989 to 1998, establishing himself as one of the best running backs to ever play the game.

Sanders also retired at the age of 30 but was a 10-time Pro Bowler. He was also named to the All-Pro 10 times, six in the first team and four in the second team. If he had played his 11th season in 1999, Sanders could have broken Walter Payton's NFL rushing record.

Patrick Willis

The San Francisco 49ers linebacker quit the sport in March 2015 due to various injuries and the aspiration to retire in his prime. He was named to the Pro Bowl and All-Pro seven times in his eight-year career.