Ousmane Dembele missed training with Borussia Dortmund on Thursday and has not accounted for his absence to head coach Peter Bosz, amid reports linking the France winger with Barcelona.
Following Neymar's world-record EUR222million move to Paris Saint-Germain, Barcelona have been heavily linked with big-money moves for both Dembele and Liverpool midfielder Philippe Coutinho.
While Liverpool boss Jurgen Klopp insists the Premier League club would stand firm and had no need to sell Coutinho to Barca, Dembele's future was thrown into fresh doubt when Bosz told a news conference ahead of Saturday's DFB-Pokal tie at Rielasingen-Arlen the 20-year-old had skipped preparation without permission.
"Ousmane Dembele was not in training. We do not know why. We tried to reach him but were unable to," Bosz said.
"I talked to Dembele yesterday [Wednesday]. He told me he was in Paris with his friends. He did not say anything about a transfer."
He added: "There was no sign that Ousmane Dembele would not be here. We hope nothing terrible has happened."