The ruble has fallen by almost a third against the dollar since the start of the year, accompanied by a fall in the price of oil, a crucial factor for Russia's state budget.
Organizing committee leader Alexei Sorokin told local media on Wednesday they "can't do without" purchases from abroad in World Cup construction but will try to replace some imported goods with local production.
Sorokin said the Russian government has "no big desire" to raise the budget to compensate for the ruble's fall, and that spending cuts are off the menu.
"It would be a different World Cup, or not even a World Cup at all" if cuts are made to the budget, Sorokin said. "There's nothing left to be cut."
The World Cup budget is 664 billion rubles ($16 billion), mostly from public funds, although the headline budget figure does not include commitments by state companies to build many new transport links.
When Russia won the right to host the tournament in 2010, President Vladimir Putin said it would cost around $10 billion.
Sports Minister Vitaly Mutko sounded a warning on costs Wednesday when he said that projected increases for the planned stadium in the city of Kaliningrad, one of 12 World Cup arenas, "don't satisfy" the government.
Sorokin suggested the Kaliningrad stadium should be moved to another location in the city, away from its current site on an island, where soft ground is reportedly likely to inflate building costs. The issue must be solved by the end of the week, Sorokin was quoted as saying.