A day earlier he had warned that the man carrying China's biggest hopes for a track gold was on far from peak form.
"He has been fighting and fighting until the last moment"
Sun, whose relationship with Liu is often described as like that of a father and son, broke down in tears as he spoke of his disappointment.
"He has been fighting and fighting until the last moment," he said, aware of the massive build-up in Chinese media that had predeeded Liu's appearance in Beijing.
Liu, who was China's best hope of an athletics gold, shot to fame and fortune four years ago following his unexpected gold in the Athens games.
He became the first Chinese athlete to achieve a "triple crown" of athletics, adding the 2007 110m hurdles world championship title to his 2004 Athens gold and his world record of 12.88 seconds set in 2006.
That record was bettered earlier this year by Cuba's Dayron Robles.
Signs of trouble
|Liu had faced huge pressure to compete in Beijing [EPA]
On a sunny Beijing morning he had received a thunderous welcome from a packed the home crowd as he came on to the track to defend his title.
The first signs of trouble on Monday came in the pre-race warmup when Liu stopped after two hurdles. He was then seen crouching down before walking gingerly back to the starting area.
Minutes later, following a false start, pictures on Chinese TV and shown on big screens inside the stadium showed the 25-year-old hobble back into changing rooms as the stadium descended into stunned silence.
Wih Liu's dreams of Beijing gold over before they had even begun, the capacity crowd immediately began to thin out as the man many millions of Chinese regard as a national hero left the stadium.
Alongside basketball giant Yao Ming, Liu is China's most popular sports star and he had faced a huge weight of expectation to repeat his 2004 Athens triumph on home soil.
His face features on advertising boards across the country, promoting international brands such as Nike, Coca Cola and Cadillac as well as, more controversially, a foundation run by one of China's biggest cigarette manufacturers.
A national survey last year of more than a million Chinese found the country's most popular Olympic dream was to witness Liu winning gold at the Bird's Nest stadium.
In the run-up to the Beijing Olympics one Chinese insurance company reportedly offered to insure Liu's legs for almost $14m.
Liu replied that his legs were priceless.
His early exit on Monday followed an earlier heat that saw the departure of US two-time silver medallist Terrence Trammell, who himself limped off the track clutching his lower left leg.
Liu and Tramell's misfortune puts the spotlight on Dayron Robles, the Cuban 21-year-old world record holder, who came first in his heat with a perfect run of 13.39 seconds, not touching a single hurdle.