Schalke sporting director Horst Heldt is unwilling to sell defender Kyriakos Papadopoulos, with the club rejecting a bid from Zenit St Petersburg.
Papadopoulos, 20, has been the subject of a €15 million offer from Russian champions Zenit, but Heldt is determined to keep hold of the Greece international.
"They have made an offer and are being very persistent but we do not want to lose the player," Heldt told He told kicker.
Heldt was speaking after Schalke opened their Bundesliga campaign with a 2-2 draw at Hannover on Sunday.
Midfielder Lewis Holtby, who grabbed Schalke's second goal after Klaas Jan Huntelaar had cancelled out Felipe's opener, said: "I am disappointed. We were clearly the better team and controlled the game, making plenty of opportunities. But we conceded two stupid goals.''
Adrian Nikci grabbed a late equaliser for Hannover, whose coach Mirko Slomka was pleased with a point.
"I am very happy with one point as it is a point gained. Schalke were very dominant in the second half and I am pleased we hit back after the setback of going behind.''