US Republican and Democratic senators have prepared the bill seeking to punish Russia for meddling in US elections and Russia's role in the Ukraine crisis. The bill is a tougher version of a proposal that failed to pass last year, but Russian officials have shrugged off the risk.
"The sanctions are driving the currency lower. Also the rouble was among the best performing currencies in January and concerns about the sanctions is prompting investors to take positions out," said Petr Krpata, chief EMEA FX and interest strategist at ING in London.
At 1001 GMT, the rouble was 0.5 percent weaker against the dollar at 66.81. It lost 0.5 percent to trade at 75.30 versus the euro.
The Kremlin said Russia's economy could cope with any new US sanctions. "Our economy has long been under various sanctions. Our economy has learnt to preserve macroeconomic stability in conditions of these sanctions," Kremlin spokesman Dmitry Peskov said on Thursday.
"Our economy has learnt to provide growth in a whole series of sectors despite such unfair restrictive measures. Thus, our economy has already developed a certain resilience."
Russia has the tools to shield its economy from possible new US sanctions, and the central bank and finance ministry have already created a buffer to protect Russian banks, the Russian finance minister said.
However, traders said that more downside for the currency could be expected if the sanctions are extended to holders of Russian debt.
Russia five-year credit default swaps (CDS), the cost of insuring exposure to its debt, jumped to a one-month high with Russian dollar bond prices falling across the curve.
The rouble was falling despite a 1.4 percent growth in Brent crude oil, a global benchmark for Russia's main export, which usually supports Russian rouble.
Rouble implied volatility gauges saw their biggest jump in almost three months.
Russian stock indexes were down: the dollar-denominated RTS index fell 2.3 percent, while the rouble-based MOEX Russian index was 0.7 percent lower with Russian banks being the worst performers in the index.
Shares at Russian top lender Sberbank fell 3.6 percent. Its chief executive, German Gref, said that according to his information major Russian banks were not included in the new sanctions bill, but added that one should prepare for unfavourable situations.