"Borussia Dortmund have decided to maintain the player Ousmane Dembele's suspension from team training until further notice," the Bundesliga outfit said in a statement.
Dembele was sanctioned after he failed to show up for practice on Thursday, the same day Dortmund announced they had rejected Barca's opening offer for the France international.
he youngster was fined and initially suspended until Monday, missing Dortmund's 4-0 win over Rielasingen-Arlen on Saturday.
"Our focus is now on a concentrated preparation of the team for the Bundesliga opening match in Wolfsburg this coming weekend," Dortmund's sporting director Michael Zorc said in a statement.
"Ousmane Dembele of course has the option to train separately from the group."
Dembele, who at the age of just 20 is considered one of the top talents in Europe, has been hotly pursued by the Spanish giants to fill the void left by Neymar's move to Paris Saint-Germain for a world-record 222 million euros ($260 million).
German tabloid Bild has reported that Dortmund want an eye-watering 150 million euros ($175 million) for their rising star, a price Barca have bristled at.
Dembele himself has made clear he is keen to join the Catalans, and German media have suggested his no-show at training may have been intended to put pressure on the negotiations.
Dortmund said the initial bid made by Barca did not reflect the young winger's "extraordinary" value or the current state of the transfer market.