Schalke have asked Mesut Ozil to return excess wage payments after contract talks between club and player broke down.
Schalke had come to a verbal agreement with the 19-year-old midfielder over a new deal until 2011 that would have seen the player's wages increase to over one million euros per annum.
The Gelsenkirchen-based club agreed to increase Ozil's wages with immediate effect but the youngster has since refused to sign the contract amid reported interest from other clubs.
Schalke general manager Andreas Muller told Bild newspaper: "We agreed the contract and shook hands and increased his wage immediately.
"Now, however, we have to accept that Mesut is not going to put his signature on the contract and so we have demanded he balances the overpayments off.
"If there is another club offering him more, then he should just tell us honestly. I am no longer prepared to have him walking all over us."