T44 world champion sprinter Richard Browne has pulled out of the Paralympic Games and ended his season.
The American, 24, is the world record holder for both the 100m and 200m and among the biggest names in the sport.
The single-leg amputee has told US Paralympics he is not "mentally and physically prepared to compete at the level I am capable of".
He finished second behind Britain's Jonnie Peacock in the T44 100m at the 2012 Paralympics in London.
Browne had been suffering with a hamstring injury and did not compete in last weekend's US trials - however he was still eligible to be considered for discretionary selection.
He suffered broken ribs and concussion in a car crash in January, but returned to training shortly afterwards.
Browne's rivalry with Peacock was expected to be one of the highlights of the Rio Paralympics.
However, he said in an email sent to US Paralympics that his 2016 season was over and he would now focus on 2017.