The Bundesliga giants suspended the 20-year-old indefinitely in August when he boycotted training in protest after an initial bid from Barca was rejected.
Reports suggest that the Blaugrana have had an improved £119m offer turned down, Dortmund supposedly holding out for a bid closer to £140m.
"We are prepared to sell him and what we want is on the table," Dortmund CEO Hans-Joachim Watzke is quoted as saying by Sky Sports News.
"When it's not met, Dembele will stay with us. We will not negotiate."
Barca are seeking a marquee signing in attack to fill the boots of Neymar, who left for Paris Saint-Germain this summer for a record £200m.
Dembele, who has spent just one season at Dortmund following his move from Rennes, is contracted to the club until 2021.