It is not known where the raccoon first boarded the ship, but it is thought to have made the journey unnoticed among cargo.
Staff reportedly spotted the animal shortly after the vessel arrived in Southampton.
Wild raccoons are native of North America and are not generally domesticated.
Some are found living in the wild in central Europe after escaping from fur farms in Germany in the 1930s. It is estimated as many as 1.5 million now live in Germany, external.
While they appear harmless or even playful, they can be unpredictable and carry serious diseases.
In March, a red fox made a transatlantic journey in the opposite direction, sneaking onto a cargo ship in Southampton and ending up in New York. It was put into the care of New York’s Bronx Zoo.
A spokesperson for the RSPCA animal welfare charity said that despite some reports, it “had no dealings with the raccoon”.