Borussia Dortmund boss Peter Bosz admits he is unaware of the whereabouts of midfielder Ousmane Dembele.
Dembele missed first-team training on Thursday and Bosz revealed the France international had not answered his phone when contacted by the club.
The 20-year-old is a reported target for Barcelona, along with Liverpool midfielder Philippe Coutinho, as the Spanish club aim to find a replacement for Neymar following his £198m move to Paris Saint-Germain.
"Dembele wasn't at training today. I have no idea why he wasn't there. We tried to reach him but couldn't," Bosz said.
"First I have to talk to Dembele, then he has to explain to me why he wasn't here today. I hope nothing serious happened."
Dortmund have previously insisted Dembele is not for sale, although Sky in Germany understands he would be allowed to leave for £135m.
Dembele scored 10 goals in 49 appearances last season after joining Dortmund for £13m from Rennes and helped the club win the DFB-Pokal Cup.
Dortmund are a listed company and any offer for Dembele would have to be reported to the Frankfurt Stock Exchange.