"Stoke City came again to us. But we have sent a clear signal that we will not let him leave even at a high sum. We would not find a suitable replacement for him," Dufner said at a press conference.
"But we must never say never in football.
"I fear that Stoke will not give up. However, we have made it clear to them that we will not let him go."
For the big stories and the banter follow us on Twitter: @tribalfootball