Hertha Berlin fear Croatian defender Josip Simunic could leave the club at the end of the season.
Simunic, who has been with Hertha since 2000, has two years left to run on his contract, but has a buy-out clause of 6.5million euros (£6million).
He was linked with a move to Fulham last summer and could again be a target for Premier League clubs after another impressive campaign.
The Bundesliga leaders' general manager Dieter Hoeness has conceded that the club would be powerless to prevent Simunic from leaving, but is trying to put a positive spin on such a scenario.
"The chance is growing all the time that other teams are getting aware of him," Hoeness told Bild.
"Joe is one of the best defenders in Europe, although some had doubted his Bundesliga quality not too long ago. Now, everyone witnesses his skills, he possesses top ability.
"Selling top players is always a chance to buy a team, of course, and we have sold some players to build up our current team.
"Selling players and buying a couple of new ones for a smaller amount of money is still a very possible scenario for the future."