Chairman Bernd Hoffmann says on Hamburg's website that Madrid had offered 2 million euros ($2.7 million) plus a friendly match for the 34-year-old striker but the Bundesliga club rejected the offer "again and for the last time" on Sunday.
Hoffmann says Hamburg wants to do everything to secure a place in international competition next season and it is "unthinkable" to let Van Nistelrooy go.
Van Nistelrooy joined Hamburg from Madrid a year ago.
Hamburg is currently sixth in the Bundesliga, 17 points behind leader Borussia Dortmund.
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