China's champion hurdler Liu Xiang made a start in London but crashed at the first hurdle in the opening round and again injured his Achilles tendon.
He sensationally withdrew before the start of the 110 metres in Beijing four years ago.
The Athens gold medalist left the London Stadium in a wheelchair, with a suspected ruptured tendon.
American Aries Merritt, who is now favourite for the gold medal, says the loss of one of the all time great hurdlers is a tragedy for the event.
