In a statement , Dortmund said the particular 28-year-old had sensed unwell during a training camp in Switzerland on Monday plus underwent a number of healthcare examinations.
He has today returned to Australia where he will go through more tests at a specialist medical service over the coming times.
“This news these days came as a shock to Sébastien Haller and everyone else, ” said Dortmund’s wearing director Sebastian Kehl.
“The entire BVB household hopes that Sébastien makes a full recuperation as soon as possible and that we can give him a hug once again soon.
“We’ll do everything in our power to ensure that this individual receives the best possible therapy. ”
Haller, who has yet in order to publicly comment, only joined Dortmund previously this month right after an impressive spell with Dutch giant Ajax.
The Ivory Coast international scored forty seven goals in sixty six games for their former club during an 18 30 days spell, 11 which came in the Winners League.
Dortmund requested that Haller’s privacy be respected plus said it would provide an update when more information is available.