"I doubt that the ISS crew will be increased to six people from next year because the final decision has not been taken yet," Roscosmos head Anatoly Perminov said. "All countries participating in the ISS program have to decide it."
He said he would be discussing the issue next week at a meeting with the head of the European Space Agency, Jean-Jacques Dordain.
Russia is due to launch a crew of three to the International Space Station on Sunday. U.S. astronaut Mike Fincke, Russian cosmonaut Yury Lonchakov and U.S. space tourist Richard Garriott are scheduled to lift off at 11:01 a.m. Moscow time [07:01 GMT].