Ajax goalkeeper Andre Onana has been suspended for 12 months by UEFA after he failed a doping test last October.

The suspension is effective as of February 5, and will apply to all football activities at both national and international level.

An out-of-competition check found Furosemide in the Cameroon international's urine, but Ajax claim Onana took it "unwittingly" after feeling unwell.

"On the morning of 30 October Onana did not feel well. He wanted to take a tablet. Unwittingly, however, he took Lasimac, a drug that his wife had previously been prescribed," an Ajax statement said.

Ajax said they would appeal the ruling at the Court of Arbitration for Sport (CAS).

The club added: "Onana made a mistake with the product and mistakenly took his wife's medicine, which ultimately led to UEFA's action against the goalkeeper. The football association's disciplinary body ruled that he did not intend to cheat. However, the European Football Association believes that, according to the prevailing anti-doping rules, an athlete has a duty at all times to ensure that no prohibited substances enter the body."

Onana and Ajax will appeal the ruling at the Court of Arbitration for Sport (CAS).

Ajax's managing director Edwin van der Sar said: "We explicitly renounce performance-enhancing drugs; we stand for a clean sport. This is a terrible setback, for Andre himself but certainly also for us as a club.

"Andre is a top goalkeeper who has proven his worth for Ajax for many years and is very popular with the fans. We had hoped for a conditional suspension or a much shorter one than this twelve months, because it was demonstrably not meant to strengthen his body and thus improve his performance."

Ajax currently lead the way in the Eredivisie, holding a seven-point lead over PSV Eindhoven, while in the Europa League they face Lille in the round of 32 later this month.

The loss of Onana, unless the ban is overturned, will come as a huge blow given the goalkeeper has been an integral member of the side for five years.

After coming through the ranks at Barcelona, Onana joined Ajax in 2015, and this season he had kept nine clean sheets in 20 league games.

He also played every minute of their Champions League group-stage campaign, where they finished third Liverpool and Atalanta to drop down to the Europa League.