Dortmund's chief executive Hans-Joachim Watzke has announced the deal, although not yet complete, is "on its way", with Barca reportedly set to pay as much as €150million for the France international.
Dembele has been suspended from selection contention indefinitely by Dortmund after failing to report for training in the wake of Barca having a bid turned down for the 20-year-old forward, who has been identified as a potential replacement for Neymar, the Brazil international having left Camp Nou to join Paris Saint-Germain for a world-record €222m.
Addressing the media ahead of his team's Bundesliga match at home to Hertha Berlin, Bosz acknowledged that disruptions caused by the impending closure of the transfer window are inevitable for many clubs.
"As a coach you know there's uncertainty until August 31st," he said.
"We have to concentrate as best we can on the players who are available to us.
"[Sporting director Michael] Zorc, Watzke and I work very closely on transfers. We have a good communication."
Having recovered from seven months out due to a metabolic disorder, Mario Gotze made a long-awaited return to the Dortmund team by starting the 3-0 win away to Wolfsburg last week.
Despite being substituted in the 61st minute, there have already been calls for the attacking midfielder, who scored the extra-time winner in the 2014 World Cup final victory over Argentina, to return to the Germany squad ahead of qualifying matches against Czech Republic and Norway early next month.
But Bosz hopes Joachim Low will not call on the 25-year-old just yet.
He said: "Gotze won't play 90 minutes, even if he maybe could. We need to be careful. He's doing well.
"I think it's better for Mario to stay away from national team for now when he's not fit to play full 90 minutes for us."
"It's not an easy draw but an interesting draw," he said.
"Real Madrid are probably the best team in the world at the moment."
According to Bosz, Marcel Schmelzer is making good progress in his recovery from an ankle ligament injury but will not be available against Hertha.