South Korean side FC Seoul have knocked back a reported £1.7m bid from Celtic for promising midfielder Ki Sung-yong, saying the transfer was "non-negotiable" at the moment.
Seoul have recently sold Lee Chung-yong to Premier League side Bolton and are reluctant to let another one of their highly-rated prospects leave at this stage of the season.
"We have never stood in the way of our players signing for foreign clubs," an FC Seoul spokesman said by telephone on Wednesday. "However, Ki is still under contract to us and the season is not over yet, so the transfer is non-negotiable at the moment."
Celtic were keen to land the 20-year-old before the end of the summer transfer window in Europe but the timing was bad for Seoul, who are top of the domestic K-League with half the season remaining.
"That's impossible for us, because he's such a vital player to the team and our team is currently doing very well," the spokesman added.
"This is different from Lee Chung-yong's case because our transfer window is now closed and we would be unable to fill the void if we sent Ki to Celtic."
Ki's agent, Chun Yong-joon of IB Sports, said on Wednesday that the offer had been made on August 17 but they were unable to reveal any other details as negotiations were still underway.