Dembele has been strongly linked with Barca, who are seeking a replacement for Neymar following the Brazil international's world-record €222 million move to Paris Saint-Germain.
But Dortmund CEO Hans-Joachim Watzke has insisted it will take more than €100m to tempt his side into allowing the 20-year-old to leave Signal Iduna Park.
And Zorc insists there is nothing in a report from France that claimed forward Dembele has reached a long-term agreement over personal terms with Barca.
"I am not aware of a commitment," he told reporters after Dortmund beat Rot-Weiss Erfurt 5-2 in a pre-season friendly.
Dembele said last week it was a "pleasure" to be linked with Barca and expressed his surprise at Neymar's decision to leave for PSG.
The France international only joined Dortmund in 2016 in a move from Rennes, impressing enough in his debut campaign in Germany to be named in the Bundesliga Team of the Season, as well as winning the man-of-the match award in the club's DFB-Pokal final victory.