Tomas Dvorak, three times world champion and former world record holder, pulled out of the Olympic decathlon after the opening 100 metres on Monday with an injured ankle.
The 32-year-old Czech, who has a personal best of 10.54 seconds in the 100, managed only 11.53 in the first heat.
His right knee was strapped but it appeared to be his right ankle causing the problems as he removed his shoe and limped heavily away from the arena.
He then failed to appear for the second event, the long jump.
Dvorak won the world title three times in succession in 1995, 1997 and 2001 and finished fourth last year.
He was an Olympic bronze medallist in 1996 and finished sixth in 2000 after being hampered by a hamstring strain.
