Earlier in the day, a source told Sputnik that the US did not grant Chub a visa. The cosmonaut, who joined the Russian crew in 2012, was to take training at the Johnson Space Center before his first flight to the ISS planned for 2023.
"The situation puts under question the safety of the Russian cosmonaut's stay at the ISS and the safety of the American segment of the station due to the unpreparedness of the Russian cosmonaut in the event of an emergency," the Roscosmos press service told reporters.
Chub needs an visa to take part in the first 5-week session at the Johnson Space Center to familiarize himself with the US segment at the ISS, the space agency added.
"Without lectures and practical exercises on the layout of the US segment, getting familiar with the operation of its systems, understanding the interaction between the systems of the American and Russian segments, as well as taking a course on actions in the event of emergency, the space flight is basically impossible," Roscosmos said.
The US Embassy in Moscow does its best to continue issuing visas to Russian cosmonauts even given the limited staff, but cannot comment on separate cases of visa processing, the spokesperson of the agency, Jason Rebholz, told Sputnik.