"Medical tests are scheduled for the end of December but Ms Brightman has not confirmed her arrival yet," Igor Ushakov told TASS.
A source at the Russian cosmonaut training center said earlier that Brightman, 54, will not be allowed to start her pre-flight training in mid-January without permission of medics.
Brightman's flight is scheduled for September 1-11, 2015.
The Phantom of the Opera star who announced her plans to go into orbit in 2012 may become the first professional singer in space and the eighth space tourist to visit the International Space Station.
The cost of her flight remains a commercial secret but sources have suggested that it was dozens of millions of dollars.