Former Olympic gold medalist Shawn Johnson has retired from gymnastics after failing to come back from a knee injury.
The 20-year-old American was attempting to compete in the London Olympics this summer but a knee injury has blighted her training, eventually leading her to retirement.
"It has become obvious that my left knee is not able to sustain the demands of gymnastics any longer," said Johnson. "All I can do now is gracefully retire and thank everyone who has believed in me and my journey.
"I am announcing this now so the focus for the next three weeks will be on the incredibly talented gymnasts who are trying to make our 2012 Olympic team."
Johnson has accumulated four Olympic medals and three World Championship titles in her career.
