The International Olympic Committee (IOC) has asked South Korea to bar footballer Park Jong-woo from the bronze medal ceremony after he held up a political message after the team beat Japan.
The slogan was said to refer to a long-running dispute about islands which both South Korea and Japan claim.
The IOC says it is holding an inquiry.
Friday’s match came hours after South Korea’s president visited the islands, known as Dokdo in South Korea and as Takeshima in Japan, sparking a row.
The move prompted Japan to recall its ambassador in Seoul.
South Korea won the Olympic football bronze medal by beating Japan 2-0.
The IOC says that after the game, a player was photographed brandishing a sign allegedly asserting South Korea’s sovereignty over the islands.
The committee urged the South Korean Olympic committee to take “swift action on this issue” and said the player should not be present at the medal ceremony, which took place on Saturday.
A Korean Football Association official later named him as Park Jong-woo, 23 – who was not present at the ceremony.
Football’s governing body, FIFA, said it had opened a separate investigation to discipline him.
The official told South Korea’s Yonhap news agency that Park Jong-woo had taken the sign – which reportedly read “Dokdo is our land” – from a fan after the match, stressing that the incident was not pre-planned.
“Park was running around with the banner which he got from the crowd. We saw the message on the banner so we quickly took it from him,” the unnamed official is quoted as saying.
The statutes of both the IOC and FIFA prohibit political statements by athletes and players.
Friday’s visit by South Korean President Lee Myung-bak to the islands was strongly criticized by Japanese Prime Minister Yoshihiko Noda.
“It is contrary to our nation’s stance that Takeshima is historically – and under international law – an integral part of our national territory, and is completely unacceptable,” PM Yoshihiko Noda said.
The uninhabited islands, which are roughly equidistant from the two countries, are small but lie in fishing grounds which could also contain large gas deposits.