André Onana was suspended for a year on Friday because the Ajax goalkeeper has tested positive for furosemide.
What does that drug do, and why is it on the banned list?
Herman Ram, chairman of the Dutch Doping Authority explains.
"It is not the case that furosemide promotes sports performance", Ram told NU.nl.
"Furosemide is a water pill that ensures accelerated moisture secretion."
"It is on the doping list because it can mask other prohibited substances. Because you excrete more urine faster and more, those other substances disappear from your body faster."
Ajax reports that the substance got into Onana's body, after the goalkeeper accidentally swallowed a medicine from his wife.
The Ajax goalkeeper is certainly not the first athlete to be suspended for the use of furosemide.
"I don't immediately have figures to hand, but it does happen regularly. Internationally, but also in the Netherlands," says Ram.
"It is a substance that occurs in medicines that are available to everyone. As a result, it almost automatically occurs more often that there are athletes who get this in the body."
See also: Doping Authority: Punishment Onana is mild because there was no intent
Ajax challenges suspension at CAS
Due to his suspension, Onana (24) is not allowed to play matches both nationally and internationally.
Ajax immediately announced that it would appeal to the CAS international criminal court.
With the penalty of one year, UEFA has already taken into account the unintentional use of the substance.
Athletes are usually suspended for four years if they are shown to use furosemide on purpose.