Dembele has been linked with Barca, who are seeking to offset the departure of Neymar following the Brazilian's world-record move to Paris Saint-Germain last week.
However, Zorc insisted it will take more than €100m to pry the 20-year-old Dembele away from Signal Iduna Park.
"I am not aware of a commitment," he told reporters after the Bundesliga outfit beat Rot-Weiss Erfurt 5-2 in a pre-season friendly.
Zorc, however, expects speculation surrounding Dembele's future to continue.
"This will surely accompany us for a while," he said. "It makes no sense to comment on these permanent rumours every time."
Dembele shone in his first season with Dortmund following his arrival from Rennes last term, netting 10 goals and providing 21 assists in 49 appearances in all competitions. He was also named man of the match in the club's DFL-Supercup final victory.