Dortmund announced that medical tests to see why Goetze had been suffering from repeated injury had revealed 'metabolic disturbances'.
Borussia Dortmund said Tuesday they do not expect Mario Goetze to return anytime soon as Germany's World Cup winner battles with a unspecified metabolism disorder.
"This will not be a short-term issue," Dortmund's CEO Hans-Joachim Watzke told SID, an AFP subsidiary.
Dortmund announced on Monday that medical tests to see why Goetze had been suffering from repeated injury and a lack of form had revealed 'metabolic disturbances'.
The exact disorder has not been revealed and the club has asked for their star to have privacy as he struggles to regain his health.
"We wish to know, in the special interest concerning Mario Goetze, that the privacy of this young person will be respected and observed," Dortmund's press spokesman Sascha Fligge told SID.
The 24-year-old became Germany's hero when he scored in extra-time of the 2014 World Cup final to seal a 1-0 win over Argentina and Franz Beckenbauer once described him as 'Germany's (Lionel) Messi'.
Last July, Dortmund paid 22 million euros ($23m) to buy Goetze back from Bayern, having been forced to sell him in 2013 for 37 million euros after the Bavarians triggered a release clause.
However, poor form and injury meant he has played just six games over the 90 minutes this season, which had drawn heavy recent criticism.
Ex-Germany captain Lothar Matthaeus suggested last week that Goetze should "move to China" if he keeps failing to win a first-team place at Dortmund, but has softened his stance since illness was revealed.
"The good thing is that one now knows the cause and can treat it," said Matthaeus.
"Against this background, one has to, of course, evaluate his performances differently than without this knowledge."
Goetze was outstanding in the 2011/12 season when Dortmund won the German league and cup double.
His performances in the attacking midfield role then helped Dortmund reach the 2013 Champions League final, but he missed the 2-1 defeat to Bayern at Wembley with injury.
He then endured three difficult years at Bayern, failing to hold down a first-team place and was often left on the bench by coach Pep Guardiola, until returning to Dortmund this season.
Critics questioned whether he was mentally strong enough to cope with life at star-studded Bayern and said he had returned to Dortmund as a shadow of the player he once was.
So there is some relief at Borussia that an illness has been diagnosed.
"We are glad that we now know the reasons for Mario's complaints," said Dortmund's director of sport Michael Zorc.
