Gazprom said it was halting the operation of another gas turbine at a Nord Stream 1 compressor station due to a "technical condition of the engine".
It said that from 4am on Wednesday gas supplies would fall to 33 million cubic metres per day, cutting daily gas production to 20 per cent.
Following Gazprom’s announcement, Germany’s economy ministry said it was “monitoring the situation very closely”.
“According to our information, there is no technical reason for a reduction in deliveries,” it added.
In his nightly video address to the Ukrainian people on Monday, Mr Zelensky said the decision was “on purpose” and called on EU leaders to hit Russia was tougher sanctions.
The Kremlin insists it is a reliable energy partner, and says Western sanctions are responsible for the recent disruption of gas supplies to the EU.
It comes amid fears that Russia could cut off the taps to Europe completely.
The Nord Stream 1 pipeline, which accounts for more than a third of Russian gas exports to the EU, resumed operations last week following a 10-day annual maintenance break.
Running well under its normal capacity for weeks, an EU official has warned Russia is "using energy as a weapon".
EU Commission President Ursula von der Leyen said: "Russia is blackmailing us. Russia is using energy as a weapon.
"And therefore, in any event, whether it’s a partial, major cut-off of Russian gas or a total cut-off of Russian gas, Europe needs to be ready."
In response, EU member states have agreed to a deal that will see gas consumption reduced by 15 per cent, in order to build up stores over the winter in case supplies are reduced further or stopped in their entirety.
However the controversial plans have resulted in exemptions for some member states after original proposals were met with widespread resistance.
Nations such as Malta, Cyprus and Ireland, that are not connected to the wider European gas network will be offered a reprieve.
Meanwhile, Spain and Portugal, two of the biggest opponents to the plans, were also handed reprieves from mandatory cuts.
Hungary was the only EU member state to officially vote against the deal.