South Korean football officials are investigating revelations that four senior players, including captain Lee Woon-jae and Middlesbrough striker Lee Dong-gook, were involved in drinking and visiting prostitutes ahead of an important Asian Cup match in July.
Seoul-based agency Newsis reported that Lee Woon-jae, Kim Sang-sik, Woo Sung-yong and Lee Dong-gook drank until the early hours of July 14 at a brothel in Jakarta, where the national team was based.
On July 15, South Korea suffered an upset, 2-1 loss to Bahrain to drop to the bottom of Group D.
The players visited the brothel again on the evening of July 16, the Newsis report said.
Three of the players started in the shock defeat at Jakarta, with Woo making a second half substitute appearance.
South Korea captain Lee Woon-jae made a tearful apology at a press conference with Woo at Korean Football Association headquarters.
"I am so sorry," Lee said.
"As captain, it is my responsibility, the other players did nothing wrong. I will accept any punishment that comes my way."
The KFA will investigate the matter ahead of taking action against the players involved, it said in a public apology posted on its Website.
"We would like to say very sorry to the fans," the statement read.
"We will investigate further to discover the facts and will then take appropriate action."
Lee Dong-gook, who signed for Premier League club Middlesbrough in January, and Kim Sang-sik have yet to make any statement to the press.
South Korea reached the semifinal of the competition, losing to Iraq on penalties.