South Korea's quest for its first Olympic football medal took another hit here on Tuesday as midfielder Han Kook-young went down with an injury just days before the competition's start.

Hong Myung-bo, head coach of the men's football squad, said Han suffered a hairline fracture on his left foot. He'd been complaining of pain since early Monday, Hong added.

Han has been replaced by Jung Woo-young, who mans the midfield for Kyoto Purple Sanga in Japan's J-League. Under the competition rule, teams can replace injured members at least 24 hours before their first contest.

South Korea takes on Mexico on Thursday, a day before the opening ceremony of the London Olympics, and will later face Switzerland and Gabon in group stage.

South Korea has already been bit by the injury bug. Weeks before South Korea completed its roster of 18 players on June 29, the team lost former team captain and defensive leader Hong Jeong-ho to a knee injury. Hong's absence forced coach Hong to use one of his three wild cards -- for players over the Olympic age limit of 23 -- on a defensive back.

Then on July 12, defender Jang Hyun-soo went down with a knee injury and was replaced by Kim Kee-hee.

South Korea, playing in its seventh straight Olympics and ninth overall, has never won a football medal in the quadrennial competition. The nation has progressed beyond the first round only twice before. (Yonhap News)