Russia may stop giving gas to Europe this winter according to the International Energy Agency.
Europe needs to work on contingency plans in case of a complete shutdown, according to Fatih Birol.
Several European countries said they received less Russian gas than they thought.
Russian officials blame technical issues.
Europe used to import 40% of its natural gas from Russia, but that has fallen to 20% since the invasion of Ukraine.
Mr Birol thinks that the recent reductions in Russian gas supplies are strategic. The falls are making filling up gas storage more difficult for European countries.
"I wouldn't rule out Russia continuing to find different issues here and there, and continuing to find excuses to further reduce gas deliveries to Europe and maybe even cut it off completely," he said.
The flow of natural gas through the main line from Russia to Europe was only 40% of capacity. The Russian explanation that this was caused by technical issues is not believed to be true.
There are still shortfalls in gas supply across Europe. According to the Italian firm, it only received half of the gas that it was expecting from the Russian state-controlled gas giant.
According to France, it has not received Russian gas from Germany since June 15th, while other countries have had their Russian gas deliveries stopped because they refused to pay in Russian roubles.
European countries agreed to fill up their gas storage facilities in order to protect themselves from gas price fluctuations. They made a commitment to reach 80% capacity by November, with the latest data suggesting they are at about 45%.
Emergency short-term measures to reduce demand, such as increasing the use of coal-fired power stations, and prolonging the life of nuclear power plants, are now justified because of the gas crisis, according to Mr. Birol. He says drastic measures may need to be taken if the Russian gas supply were to be completely shut down.
There is a chance that Europe will need a planned and orderly rationing of gas.
"I don't say this is the base scenario, but looking at the last several months, if not several years, the experiences we have had with Russia as an energy partner, this is a scenario we cannot afford to exclude."