New Bayern Munich recruit Serdar Tasci suffered a head injury in training on Wednesday that forced him to miss his own welcome news conference.
Tasci joined Bayern on loan from Spartak Moscow on transfer deadline day, with the club retaining an option to make the move permanent in June.
The Germany international, who won the last of his 14 caps in 2010, was set to provide immediate defensive cover, with Jerome Boateng and Javi Martinez sidelined due to respective adductor and knee problems.
Attending the presentation with a Bayern shirt bearing Tasci's name and number, but without the player himself, Bayern sporting director Matthias Sammer announced the 28-year-old sustained a clash of heads and was being assessed for a possible concussion.
Sammer did not completely rule Tasci out of featuring in Saturday's match at Bayer Leverkusen.
"In training he had a collision with his head. Maybe it is a mild concussion, Sammer said.
"He may turn out [in] two or three days, that's not so bad.
"He is an experienced player who wants to grow into an important role for the national team.
"A player who brings many qualities - he is 28 but I hope he will seize this opportunity.
"Serdar is really looking forward to the experience and can help us with his character and his style of play.
"The situation was clear for everyone that we were in a difficult situation after Martinez's injury, so we decided to sign a new centre-back."
Sammer moved to deny speculation that Medhi Benatia was in line to rejoin former club Roma before Boateng's injury forced a rethink.
"We didn't want to sell Benatia," he said. "This is utter nonsense. The media claiming that we wanted to are lying.
"Only an insane club would think about this."