President Vladimir V. Putin’s demand on Wednesday that “unfriendly countries” like the United States, Britain and the European Union members pay for Russian natural gas in rubles has raised questions as to whether such a move would lead to renegotiation of some contracts.

Robert Habeck, the German minister for the economy and climate, responded by saying that the demand amounted to a breach of contract. And Francesco Giavazzi, an economic adviser to Italy’s prime minister, Mario Draghi, said at a Bloomberg Capital Market Forum in Milan: “My view is that we pay in euros because paying in rubles would be a way to avoid sanctions, so I think we keep paying in euros.”

Mr. Putin’s demand would blunt the effectiveness of sanctions over the invasion of Ukraine that are directed at undermining the value of Russia’s currency. Requiring buyers to pay in rubles would mean an increase in the demand for the currency, which, in turn, would help prop up its value.

The sanctions have driven down the value of the ruble as people have frantically rushed to turn their rubles into a more stable currency, like the dollar or the euro.

Vinicius Romano, a senior analyst at the consulting firm Rystad Energy, wrote in a market note on Thursday that “Putin has raised issues that go beyond the energy sector. With this he attempts to challenge the dominance of the euro and U.S. dollar currencies.”

“Nevertheless, it is unlikely that alternative currencies will be implemented in existing contracts,” he added. “Requiring payments in rubles will force Western companies to negotiate with sanctioned banks.”

David L. Goldwyn, who served as a State Department special envoy on energy during the Obama administration, said, “The Russians are playing a bit of a game of chicken in order to force gas buyers to prop up the ruble.”

“Buyers could refuse, and the Russians would be forced to give up sales or accept payment in the currency provided by the contract,” he added. “But it’s a serious risk for the buyers as well to refuse.”