Marco Russ has been diagnosed with a severe tumour disease, Eintracht Frankfurt have announced.
Frankfurt were notified Russ had failed a drugs test due to high levels of the hormone human chorionic gonadotropin (HCG).
The club subsequently initiated internal medical examinations which revealed the abnormal values were a result of a severe tumour disease, with the National Anti-Doping Agency (NADA) requesting further analysis.
"Eintracht Frankfurt has today [Wednesday] been notified of a positive drug test by Marco Russ by the anti-doping commission of the DFB," a Frankfurt statement read.
"In the finding there is a striking increase in the value of growth hormone HCG.
"We immediately implemented an internal examination, with a urology expert, in the late afternoon which gave a specialist medical finding of severe tumour disease, which explains the increased values.
"This finding was unfortunately confirmed in the evening by the immediately initiated blood tests from a biochemical institute.
"NADA had itself noted that the high value of the growth hormone can also be an indication of a disease and has suggested a clinical examination to protect the player."
Russ remains hopeful of participating in the Bundesliga relegation play-off against Nurnberg, the first leg of which is on Thursday.
"Despite the ... diagnosis the player declared himself ready to play, which was confirmed by the medical staff," the statement added.