The 20-year-old was initially suspended after missing training earlier in the week when Dortmund rejected a reported £90million bid from Barcelona.
Dortmund boss Peter Bosz admitted he was unaware of Dembele’s whereabouts on Thursday before later confirming he was in the German city.
Bosz, chief executive Hans-Joachim Watzke and sporting director Michael Zorc held a meeting on Saturday night and they have now decided to extend Dembele’s suspension “until further notice” and he will have to train on his own.
Zorc insists the ongoing saga is not an issue for the rest of the squad as they continue preparations ahead of their Bundesliga opener against Wolfsburg on Saturday.
"Our focus now is on preparation for the Bundesliga opening match in Wolfsburg [on 19 August]. Dembele, of course, has the opportunity to complete an individual training session outside the group,” Zorc said.