Unless the Russian government steps up its funding "the current poor state of municipal infrastructure in the host cities means the standards of infrastructure at tournament venues are likely to be lower than in the past," S&P said in a report issued Tuesday.
The Russian government estimates the total 2018 World Cup budget at $22 billion, which already is significantly higher than Brazil's budget of $13.6 billion for the 2014 World Cup.
Russia's local governments, however, have put the total cost for the 2018 World Cup at up to $43 billion, which includes new metro lines, roads, airports and utility upgrades.
But for most of them, "slowing economic growth, material spending pressure triggered by a presidential call for public salary increases and very modest fiscal flexibility" will make it difficult to find sufficient funds, Standard & Poor's said.
The Russian government has said it would restrict its World Cup support to sports-related construction.
The ratings agency encouraged the federal government to step in as it has done ahead of other international events, including the 2014 Winter Olympics in Sochi, but cautioned that Russia may find this more difficult now because of slower economic growth and higher spending.
S&P said four Russian cities should have no trouble covering their 2018 World Cup expenditures: Moscow, St. Petersburg, Kazan and Sochi. Among the remaining seven, those facing the biggest difficulties are Kaliningrad, Samara and Saransk, it said.
Russian expenditures for the 2014 Sochi Olympics are estimated at about $50 billion the most expensive Olympics ever, significantly higher than the $14.3 billion spent by London in 2012.
The ratings agency report said Russia's federal and local governments may have underestimated their World Cup costs because "budgets for large capital projects in Russia have often exceeded initial estimates." One main reason for this is Russia's rampant corruption, which is particularly high in road construction and other building projects.