Japan's Deep Impact has tested positive for a banned substance after finishing third at this month's Prix de l'Arc de Triomphe, Japanese officials said.

Traces of ipratropium, an inhaled medication that aids breathing, were detected in the horse's urine samples following tests carried out after the October 1 race in Paris.

Both Deep Impact's A and B samples tested positive for ipratropium, which is not on Japan's list of banned substances, Japan Racing Association (JRA) officials said.

Deep Impact had previously undergone treatment for respiratory problems but his handlers were aware that ipratropium was banned in Europe, JRA officials said.

The Japanese Triple Crown winner was widely considered the best horse in the country's racing history.

Around 5,000 Japanese race fans sparked a betting frenzy in Paris but Deep Impact narrowly failed to live up to his billing as favourite under jockey Yutaka Take.

The four-year-old colt had won 10 of 11 starts in Japan and had been heavily tipped to become the first non-European horse to win the Arc.