- Summary- Russian rouble plunges over 4% against dollar- Rouble on course for biggest 1-day drop since July- Currency hits 68.4800 vs dollar, weakest since May 11- Pressure from fears over impact of oil restrictions- This content was produced in Russia where the law restricts coverage of Russian military operations in UkraineMOSCOW, Dec 19 (Reuters) - The rouble slumped to its weakest point in more than seven months against the dollar on Monday and was on course for its biggest single-day drop since July amid fears that sanctions on Russian oil will hit the country's export revenue.Monday's drop came as Russian President Vladimir Putin visited Belarus, fanning fears in Kyiv that he intends to pressure his ex-Soviet ally to join a fresh ground offensive that would open a new front against Ukraine.That weakening stems from concerns that an oil embargo and price cap will reduce Russia's oil export revenues, increasing the budget deficit as imports gradually recover, said Alfa Capital analyst Yulia Melnikova.European Union leaders agreed to a ninth package of sanctions against Moscow last week, blacklisting nearly 200 more people and barring investment in Russia's mining industry, among others.TAX SUPPORTAnalysts expect that upcoming month-end tax payments, when exporters convert foreign currency revenue into roubles to pay local liabilities, will provide support for the rouble, but having crossed the 65 threshold for the first time since May, the currency could settle into a new, weaker range."