The 20-year-old France worldwide was fined and suspended until Monday for missing Thursday's training, but the ban has been extended indefinitely.
Dembele will be expected to train on his own while the rest of the squad prepare for their first Bundesliga game of the season against Wolfsburg next Saturday.
"Borussia Dortmund will not make any further comment at this stage".
"Ousmane Dembele has the possibility to do individual training away from the group".
Our referenced source is suggesting that the decision was taken after a meeting between the Borussia Dortmund manager Peter Bosz, the chief executive Hans-Joachim Watzke and the sporting director Michael Zorc.
Dortmund have now announced Dembele will be punished for his no-show and will be banned until after this Saturday's DFB-Pokal clash with Rielasingen-Arlen.
In a statement to the stock market, the club said: "Borussia Dortmund has chose to uphold the training suspension for the player Ousmane Dembele until further notice".
Catalan broadcaster RAC1 has reported that Real Madrid could enter the race for Dembele, while German publication kicker said on Sunday that Barca had yet to register a new bid.