Defender Yeray Álvarez, 30, is said to have left a positive doping test in connection with the European League semifinal against Manchester United in the spring.
"It was a hard blow. I could not believe it was true because I have never ever taken any prohibited substances", he writes himself in a statement on social media.
Yeray Álvarez was diagnosed with testicular cancer in 2016 and - after being cleared on two occasions - is said to have undergone a new treatment in the spring.
"Since I overcame my illness, I have been treated for alopecia (hair loss) for several years. After studying the case, we have found that the positive test was due to the fact that I unknowingly took a preventive medicine for hair loss that contained a prohibited substance", he writes further.
Athletic Club writes in a statement that they "regret the human factor" in the case and that they will show their support, but that they cannot comment further for the time being.
