Standard & Poor's Ratings Services on Monday cut its foreign-currency rating on Russia to junk for the first time in more than 10 years.

A one-notch downgrade was largely expected and priced into Russian asset prices.

"The downgrade was largely as expected," said Tim Ash, a strategist at Standard Bank. "This reflects a combination of lower oil prices, sanctions and the conflict in Ukraine with the difficult geopolitical tussle with the West which shows no sign of easing. These factors have and are expected to continue to weigh on Russia's balance sheet and overall credit matrix.

"I would expect Fitch and Moody's to follow relatively soon," he added.

But Alexey Pogorelov, Russian economist at Credit Suisse, said the downgrade "might be more damaging for the Russian assets and the ruble than everyone thinks."

Mr. Pogorelov said in recent days the pressure on the ruble has increased mainly from the geopolitical tension in the south-east of Ukraine and a threat of further sanctions.

On Dec. 23, S&P placed the country on negative watch, indicating a downgrade was likely, citing the rapid deterioration of its monetary flexibility and the impact of the weakening economy on the country's financial system.

"The outlook is already very bleak as the economy is firmly on the path that leads to recession following the sharp fall in oil and the full-scale currency crisis that unfolded in December," said Piotr Matys, a rates strategist at Rabobank.

The downgrade to junk cements the underlying trend of investors selling off their assets in Russia, which means that Russia's central bank will have to support the ruble by keeping interest rates at 17% and may have to intervene directly in the foreign exchange market, Mr. Matys said.

"If capital outflows accelerate and international reserves continue to shrink rapidly, market speculations that Russia might implement capital controls are likely to escalate," he said.

Despite the downgrade, Russia remains classified as investment-grade, based on most global fixed-income indexes' rules as the country's average rating--including S&P, Moody's Investors Service and Fitch Ratings--is triple-B-minus. But another downgrade below junk level would render Russia ineligible for most investment-grade indexes.

On Jan. 16, Moody's cut its Russia's ratings to the brink of junk territory, bringing it in line with Fitch's rating, and noted it was reviewing the country's balance sheet, particularly its foreign-currency-reserves cushion.

"Moody's caught up and they struck an appropriately negative tone when they kept Russia on review for another downgrade," said Per Hammarlund, a strategist at SEB.

He added: "Given the weakness of the ruble and the high level of local rates, international lenders and investors will be attracted to Russia if sanctions are eased. Even if they don't fully reverse net capital outflows, it will ease the burden on public finances and the pressure on" Central Bank of Russia reserves.

"In addition," Mr. Hammarlund said, "if oil prices find a floor as seems reasonable in the second or third quarter and recover towards the end of 2015, both public finances and the ruble will look better."

The ruble was trading at 67.67 to the dollar, down 3.5%.

Write to Chiara Albanese at chiara.albanese@wsj.com and Maria Armental at maria.armental@wsj.com

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