The South Korea international has been linked with Fulham and Middlesbrough and K-League club Tigers remain hopeful of cashing in on their star man.
"We have about 20 days left. Something can happen before August 31,'' Tigers vice president Kim Hyung-yong said.
"However, based on experience, it takes about one month to complete a deal but we have not had contact with the team. It is getting harder as time progresses.''