Michael Rimmer has admitted that he was "shocked" and "confused" as to why he failed to make the semi-finals of the men's 800m earlier today.
The Team GB runner could only finish fifth in his heat, despite performing well in a pre-Olympic training camp in Portugal last week.
"I'm shocked. Shocked. I just wanted to make sure I got in the top three to qualify for the semi-finals," he told BBC Sport.
"I was confident taking it on but my legs didnt have a change of gears. In Portugal at the training camp I was PBing every session. I'm confused."
The 26-year-old had been competing in the second Games of his career.