Former champion Liu Xiang's Olympic misery continued when the Chinese athlete crashed at the first barrier in the 110m hurdles heats.
Liu fell before hopping down the track, where he was embraced by his fellow competitors.
Liu Xiang is helped from the track
The 29-year-old was an icon at the Beijing Games four years ago but managed just a few strides in those heats before pulling up injured.
The former world record holder had suffered injuries going into London.
He had his right Achilles taped before the race.
Great Britain's Andy Turner, who finished third behind Liu in Daegu, won the heat in 13.42seconds before helping the stricken athlete from the track.
Turner said: "I regard him as probably the best hurdler in history and have so much respect for him. It was horrible seeing him limp off like that so you have to go and help people.
"When you [win a] medal with people you have a kind of connection and after last year in Daegu we always say 'hello' and try to have a chat in what little English he speaks.
"He's a nice guy and I wouldn't wish that on my worst enemy."
World number one Aries Merritt, from the United States, said: "It's just a tragedy for that to happen to one of the best hurdlers of all time.
"I hope he's OK. He looked fine before the race. He was happy. I don't think anything was wrong, I think he just made a small mistake and when you do that at this speed it's hard to recover."
Britain's Lawrence Clarke joined Turner in qualifying for the semi-finals but Andrew Pozzi was unable to finish his heat after pulling up after 20m with a hamstring injury.
Born: Shanghai, China, July 13, 1983
Olympics - gold (2004)
World Championships - gold (2007), silver (2005, 2011), bronze (2003)
Asian Games - gold (2002, 2006, 2010)