Russian leader Vladimir Putin has acknowledged that his country's natural gas transit deal with Ukraine will not be renewed.Sergei Guneyev/Pool/AFP via Getty ImagesRussia's natural gas transit deal with Ukraine is set to expire soon, which would cut billions in revenue.The deal's possible end affects European countries relying on Russian gas via Ukraine.Russia has shifted much of its energy exports to India and China amid Western sanctions.Russia is set to lose yet another source of income for its war chest in days — and it's Ukraine calling the shots.An agreement to let piped Russian natural gas transit via Ukraine to Europe is set to expire at the end of the year, depriving Moscow of billions of dollars in income for its wartime economy.European countries receiving gas from the pipeline have voiced concerns about the end of the supply, but Ukrainian President Volodymyr Zelenskyy has repeatedly said that the five-year agreement will not be renewed.Meanwhile, Russia has said it's ready to extend the agreement — although President Vladimir Putin said last week it's "clear" there wouldn't be a new contract.Still, the situation could change.Zelenskyy said last week that Ukraine could consider continuing the arrangement if Russia doesn't receive payments for the fuel until the war ends.On Monday, Kremlin spokesperson Dmitry Peskov said the gas transit was complicated."The situation here is very difficult, requiring greater attention," Peskov said, according to TASS state news agency.Russia is likely making $5 billion in gas sales via Ukraine this yearThe end of the five-year transit deal would be a blow for Russia, which could make about $5 billion from gas sales via Ukraine this year alone, according to Reuters' calculations based on Moscow's gas price forecast.It would also impact several European countries that still depend on Russia for gas, including Slovakia, the Czech Republic, and Austria.