Another serious injury would mean retirement, China's Liu Xiang said yesterday, as his coach expressed doubt that the recovering 110m hurdles world champion could ever reach his best times again.

The 25-year-old former world record holder and Olympic champion had surgery on a foot injury in Houston in December that robbed him of the chance to defend his title on home soil at August's Beijing Games.

"If I get injured again, I will say goodbye to the sport," Liu told the China Daily.

"I'm even considering what to do in the worst-case scenario (of getting injured again) so I don't feel too much pressure," Liu added.

Liu, who has been away from the track since hobbling out of the Bird's Nest stadium amid stunned silence on August 18, has begun light running and training over hurdles, but remains a doubt for the world championships in Berlin in August.

While the hurdler might be able to reach peak fitness again, discarding his injury fears and rediscovering his "mental resilience" after the Olympic ordeal would be another matter, Liu's coach Sun Haiping said.

"He was a top-level athlete before the injury but now his training has been badly affected and it will be difficult to run those best times again.

"If he suffered another injury, I don't think there would be any point continuing his career," Sun said.

Liu, China's first man to win an Olympic track gold, had his world mark eclipsed by Beijing champion Dayron Robles of Cuba last year.

Robles, who finished fourth behind Liu at the world championship in Osaka in 2007, will be favourite to win his first world title in Berlin.