Cameroon and Ajax goalkeeper Andre Onana was banned by UEFA for one year for a doping violation after a banned substance, Furosemide, was found in his urine.

His club, Ajax, confirmed the news in a statement on Friday adding that the ban began immediately and applied to all football activities, both national and international.

"The disciplinary body of the European football association, UEFA, has imposed a suspension of 12 months on Andre Onana for a doping violation. After an 'out of competition' check on October 30 last year, the goalkeeper found the substance Furosemide in his urine," the statement said.

However, Ajax defended the goalkeeper claiming that he had mistakenly taken his wife's medicine, Lasimac, as he sought medication to alleviate some discomfort as he was unwell.

Ajax added that UEFA agreed the 24-year-old had no intention of cheating, but it believed an athlete had a duty "at all times" to ensure that no banned substances enter their body.

Onana took to social media to defend himself arguing that he had no need to resort to doping to boost his sporting career. He also labelled the ban "excessive and disproportionate".

"Everyone knows that I lead a very healthy life, and since I started my sporting career, I have always been strongly against any use of doping and I condemn any unsportsmanlike conduct," he wrote.

The Dutch champions and Onana confirmed they will appeal the decision to the Court of Arbitration for Sport (CAS).

Ajax's managing director Edwin van der Sar described the ruling as a "terrible setback" for both player and club.

"We had hoped for a conditional suspension or for a suspension much shorter than these twelve months, because it was arguably not intended to strengthen his body and thus improve his performance," Van der Sar said.

The ban means Onana will also miss the 2021 Africa Cup of Nations, which will be hosted in his home country but rescheduled for January 2022 due to the COVID-19 pandemic.

(With input from Ajax Amsterdam)