Ajax Amsterdam goalkeeper Andre Onana has been suspended for 12 months by European soccer’s governing body UEFA for violating doping rules, the club said on Friday.

Traces of the banned substance Furosemide were found in the Cameroon international’s urine during an out-of-competition test on Oct. 30, Ajax said, leading to a year-long ban for the player from all football activities effective from Friday.

Ajax said the violation was the result of a mistake by Onana who, according to the Dutch club, accidentally took a medicine meant for his wife on the morning of Oct. 30.

Ajax said it would appeal the ban at the Court of Arbitration for Sport (CAS).

Onana’s doping ban is the second blow for Ajax within a few days after the discovery earlier this week that they had failed to register their record signing Sebastien Haller for the Europa League knockout rounds.

The 24-year old Onana has played 142 matches for Ajax since 2015 and has earned 15 caps for Cameroon.