Russian gas imports have been cut from about 130,000 cubic metres per hour to about 87,000 cubic metres.
INA said that the situation was uncertain because it was hard to predict further developments in relations between Russia and Ukraine.
As a result of a war of gas prices that broke out between the two countries, Russian state-run gas monopoly Gazprom halted gas supplies to Ukraine on Sunday, accusing Ukraine of stealing gas being transported via its territory to Western Europe.
"We do not expect problems with supply this week and the next," INA-Naftaplin sales director Natasa Vujec said, expressing hope that the situation would not last longer than two weeks.
In order to make up for the reduced supplies of Russian gas, INA has entered into talks on possible emergency imports of natural gas from Europe.
Describing the current situation in the Croatian gas supply system as stable, Vujec said that households would have absolute priority, and that gas supplies to major consumers had already been reduced.
INA appealed to all consumers to use gas sparingly.
The current rate of natural gas consumption in Croatia is about 400,000 cubic metres per hour.
Croatia produces about 60 per cent of its natural gas needs and imports the rest from Russia, according to a statement from the Ministry of the Economy.
"A prolonged reduction of gas supplies may cause problems, because it is probably impossible to find alternative suppliers, and even if we do, they will certainly be more expensive," the ministry said.