PARIS, Nov 27 (Reuters) - French far-right presidential hopeful Eric Zemmour capped a tough week on Saturday after cameras caught him giving an opponent the middle finger following a tumultuous campaign stop in Marseille. Zemmour, a former journalist known for his hardline anti-migration stance and euroscepticism, has dominated the pre-election calendar with his polarising language. Opinion polls had seen him rivalling Marine Le Pen, leader of the traditional far-right Rassemblement National party, to get into the second round of next April"s presidential election. But his campaign is stalling after various mishaps, even before he has formally announced his candidacy -- something he is expected to do at a mass rally in Paris on Dec. 5. Agence France Presse snapped Zemmour sticking his middle finger out at an opponent who had just stuck her finger out at him, and quoted Zemmour saying afterwards "and very deep". This weekend"s trip to France"s second city, Marseille, was supposed to end his pre-candidacy campaign on a positive note, but he got a frosty welcome. One walkabout barely lasted 15 minutes with local residents crying out: "Get out, Marseille anti-fascist"! Police eventually escorted him through the train station as anti-fascism protesters demanded he leave their city. "Fingergate" is likely to hurt his already stagnating poll ratings. An Elabe poll this week had already seen him lose about 2 points to between 12%-15% from two weeks ago and Le Pen rising about 2-4 points to between 20%-22%. Zemmour"s troubles started almost 10 days ago after a trip to Britain to woo investors was overshadowed by the Royal Institution of London cancelling the event. In Geneva, authorities denied him permission to hold a conference at a restaurant. He also sued gossip magazine Closer after it claimed he was expecting a baby with his chief political aide. (This story was refiled to fix typo in last paragraph)