Andy Pozzi's Olympic 110 metres hurdles debut lasted barely 20 metres as he pulled up ahead of the second hurdle before trudging disconsolately off the track at the Olympic Stadium.
The 20-year-old athlete tore a hamstring at last month's Diamond League meeting at Crystal Palace and has been unable to recover in time.
Pozzi said: "It just went coming out the blocks. It's the first time I've been full speed out of the blocks since Crystal Palace when it happened.
"I thought I could maybe manage it, but going over hurdle two it just completely wiped out and that was me (done).
"It's just so disappointing. I've run I think 12 'A' standards, I've been fit for so many races and I have been running well and it's all been centred around this. So to come here and for that to happen is heartbreaking."
His training partner Lawrence Clarke made it through, finishing second in 13.42s and Andy Turner won his heat in 13.42, but there was a major upset as China's former Olympic champion, Liu Xiang, one of the favourites for the gold medal, clattered the first hurdle and fell.
Clarke said: "I am so relieved. I have dreamt of this moment all season, for the last four years. I was determined not to come to the start line and make a hash of it."