Two sources familiar with the matter told Reuters on Thursday that no big European companies have so far started to pay for Russian gas in roubles. "Several traders, maybe more than five, have started payments," one of the sources added.

Meanwhile, a senior European Union official noted that opening an account in roubles at GazpromNank could be a breach of sanctions "at first sight."

Market reaction

These comments don't seem to be having a noticeable impact on market sentiment. As of writing, the Euro Stoxx 600 Index was up 0.9% on a daily basis.