The 22-year-old midfielder has been out of action since August with a persistent back problem and Michael Zorc has revealed that the player's condition is not improving.
The midfielder has been sidelined since aggravating a back injury during Germany's friendly with Paraguay in August but had been expected to return to action last month.
However, Dortmund's medical team has confirmed that the 22-year-old is still suffering from an inflamed nerve and the club's sporting director, Michael Zorc, has admitted that the club has no idea when Gundogan will be available for selection again.
"He is not making any progress at the moment," the Schwarzgelben legend is quoted as saying by Zeitung. "We do not know when he will be able to play again."
Gundogan, who has been capped eight times by Germany, has made just one appearance for Dortmund so far this season.