"I still have the heart, drive, and desire to compete and help the USA at the London Olympics," said Johnson. "Unfortunately, it has become obvious that my left knee is not able to sustain the demands of gymnastics any longer. All I can do now is gracefully retire and thank everyone who has believed in me and my journey."
She walks away from the sport with an Olympic gold and three silvers. Her dynamic routines in Beijing helped the U.S. earn a silver team medal, and she earned three golds at the 2007 world championships. After the Games, she also won TV's popular reality show "Dancing with the Stars."
Johnson's retirement will make the decision of the committee choosing the Olympic team a touch easier. The U.S. won the world championships in 2011 and team silver at the 2008 Olympics. Nine of the athletes competing have world or Olympic medals and are trying for the coveted five spots.
Shannon Miller, a Yahoo! Sports analyst for the upcoming London Games and a seven-time Olympic medalist, said the committee will have to make tough decisions.
"This will be a tough year filled with agonizing decisions as athletes prepare and compete. With only five spots available on the Olympic gymnastics team, athletes have to make the next two competitions [the VISA Championships and the U.S. Olympic Trials] count. Every move they make will be considered by the selection committee in determining the team. As a former athlete, I know that the Olympic trials process is more daunting and rigorous than the actual Games. That's the icing."
But even without competing in 2012, Johnson's place in U.S. gymnastics history is safe.