Schalke coach Felix Magath is not prepared to accept any offers for Jefferson Farfan in the January transfer window.
Farfan, who joined the Royal Blues from PSV Eindhoven in June 2008, has impressed in recent weeks despite the club's poor start to the Bundesliga season.
His form has reportedly attracted the attention of Valencia, Atletico Madrid and Sevilla but Magath insists the Peruvian is not for sale.
The Schalke boss told BILD: "Selling Jefferson is not an issue. And I can't imagine that he wants to change clubs."
There is still room for improvement in the 26-year-old's game, according to the former Bayern Munich and Wolfsburg boss.
"He is a class player who works hard," said Farfan. "But he also must make more goals."