Schalke will decide on the future of defender Joel Matip next month, with Sunderland and Liverpool targeting the Cameroon international.
Matip is one of several centre-halves that Sunderland have scouted over recent weeks, as Sam Allardyce looks to boost his defensive options in the January transfer window.
But Sunderland are not alone in keeping tabs on the 24-year-old, with Liverpool boss Jurgen Klopp an admirer after his days with Borussia Dortmund.
German side Schalke want to keep Matip at the club, yet he is out-of-contract at the end of the season and has rejected the offer of a new deal.
Schalke are in the midst of financial difficulties, with the Bundesliga side set to decide whether to keep Matip at the club or cash-in next month.
General manager Horst Heldt: ”Our competition is tough. We have agreed with his agents that we will make a decision in January.