Alemannia Aachen striker Szilard Nemeth has been ruled out for six months.
The former Middlesbrough star has been diagnosed with a pulmonary embolism.
The 29-year-old was recovering from pneumonia, but the condition deteriorated and now doctors have found out that he has the serious lung condition.
"It was hard for me to sleep at night. I went to hospital on Thursday to undergo an investigation and the doctors told me the diagnosis was a pulmonary embolism," Nemeth told CTK.
New Slovakian coach Jan Kocian was left shocked by the extent of the problem.
"I am shocked as I know him from the times when I was assistant coach in Kosice," he said.
"At that time, Szilard had some different health problems and I was in a real fear over his career."