Hans-Joachim Watzke has warned Bayern Munich that Mats Hummels will only be sold if they meet Borussia Dortmund's valuation.
Dortmund announced last week that their captain wants to rejoin his boyhood club Bayern at the end of the season, but they have no intention of letting the centre-back go on the cheap.
"We named our price and that is non-negotiable," Watzke told Suddeutschen Zeitung.
"They either match our asking price or the deal is off."
Hummels - who was loudly jeered by Dortmund's fans during Saturday's 5-1 win over Wolfsburg - came through the ranks at Bayern, but left the Allianz Arena for Signal Iduna Park in January 2008.
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