Naidich, who competed at last year's Olympic Games in Rio de Janeiro, has not yet been officially suspended.

The Argentine Confederation of Aquatic Sports (CADDA) decided it was best for the 26-year-old to withdraw from the event in the Hungarian capital before yesterday's 1,500 metres freestyle heats.

Naidich, who had already taken part in the 400m and 800m freestyle races, is the first athlete participating at the event to have failed a drugs test.

Confusion has surrounded the case since it was revealed as FINA have not officially confirmed the news.

According to Argentina newspaper La Nación, the CADDA has informed the country's anti-doping body (ONAD) of Naidich's failed test.

It is not yet known whether he tested positive after the 400m or 800m events.

He was 26th quickest over the longer distance and 35th fastest in the 400m.

"We have to wait for the final resolution of ONAD, because at this moment the athlete is not suspended," CADDA vice-president Raúl Araya said. 

"The one that has to suspend the swimmer is the court of Argentina and the FINA waits for that resolution.

"He agreed to withdraw from the competition. 

"And as every athlete has, he has the right to his defence. 

"We are not going to judge him in any way."

Naidich, who has represented his country in the pool for almost a decade, has denied wrongdoing.

"I'm waiting from an official communication from the association to get further details about my situation," he said.

"I was surprised that this time the result was not like it always was.

"I am distressed by all this but reassured that I have never consciously taken a forbidden substance."