Reports in the Spanish media had surfaced suggesting that Real will be given priority by the German club.
Reus is currently out injured with an ankle ligament problem and Real coach Carlo Ancelotti was fulsome in his praise of the 25-year-old earlier this week.
Sami Khedira and Toni Kroos, Reus' Germany team-mates, are already at the Santiago Bernabeu. But Dortmund chief executive Watzke was quick to rubbish any speculation of an agreement with the Spanish giants, although Reus' contract does include a buyout clause - reportedly set at €25million - which comes into effect next season.
"This is complete nonsense that there is an option right agreement," Watzke told Bild.
"Marco alone will decide where he will go.
"If he decides to make use of the clause there is nothing we can do."