LONDON - Liu Xiang's coach said on Friday the 2004 Olympic hurdles champion is being troubled with foot injury.

"His back problem is nothing to worry about, but his foot injury which has flared up is worrying me," said coach Sun Haiping at Heathrow Airport.

Sun and Liu returned to London on Friday from Germany where Liu trained for two weeks after he withdrew from a London athletics race because of back discomfort.

Liu, a Chinese sports icon, pulled out of the 2008 Olympics because of foot injury.

Sun noted anyone who clocks between 12.90 and 19.95 seconds is able to win the 110m hurdles title in London.

"We are confident despite the injury," said Sun. "But, I am a little bit worried," he added.

China's 110m hurdler Liu Xiang (R) arrives at Heathrow airport in London, Britain, on Aug 3, 2012. Liu Xiang will compete in men's 110m hurdles competition of athletics at the London 2012 Olympic Games on Aug 7. [Photo/Agencies]

China's 110m hurdler Liu Xiang arrives at Heathrow airport in London, on Aug 3, 2012. [Photo/Agencies]