Hamm is the only American man to win the world and Olympic titles
All-around gymnastics champion Paul Hamm will miss out on defending his title at the Beijing Games after he was forced to pull out with a broken hand.
Hamm, 25, had an operation after suffering the injury in May, but has not recovered sufficiently to compete.
"I put my heart and soul into my comeback and did everything I could to get ready in time," said the American.
"The team's success is most important. While I'm very disappointed, I can wait no longer to make this decision."
Hamm took two-and-a-half years out from the sport after his controversial win at the Athens Olympics, which saw three judges suspended for a mistake which secured his gold medal.
He looked to be on course for a place in Beijing when he trained with the rest of the squad earlier this month.
He performed in all six disciplines but he struggled on the parallel bars and admitted he still had pain in the hand.
"We admire Paul for making this difficult decision," said Steve Penny, president of USA Gymnastics.
"Paul's comeback this year has been phenomenal, made even more impressive following the injury to his hand."
Hamm is the only American man to win the world and Olympic titles, in 2003 and 2004, and he led the team to a silver medal in Athens, its first Olympic team medal in 20 years.
His injury leaves his main rival, two-time world champion Yang Wei of China, as hot favourite to win gold.