Dortmund have released a statement announcing that midfielder Mario Gotze will be out of action for an unspecified period due to "metabolic disorders".
The midfielder has been limited to just 11 league appearances in 2016-17 following his summer move from Bayern, with various injury problems having held him back.
The World Cup winner has endured plenty of criticism since his switch back to Dortmund, and the latest setback will do little to help his cause in proving his critics wrong on the pitch.
"The world champion has been struggling with muscular problems in recent months, leading to a thorough internal search for possible causes.
"Investigations have now revealed metabolic disorders, which make it absolutely necessary to take Gotze out of training."
Gotze has scored just two goals in all competitions so far this season but remains determined to help Thomas Tuchel's side as they battle on three fronts.
He said: "I am getting treatment and will do everything to get back into training again to help our team reach our goals."
Sporting director Michael Zorc added: "We are glad, that we now know the reasons for Mario's problems and we are convinced that he will give us an extra quality with his extraordinary skills once he has completely recovered. Everybody at the BVB will give him full support."