The star arrived at the Star City training camp last week for preliminary training - but has not yet finalised a deal to become the next space tourist.
"We're still in the early stages of negotiations, and nothing concrete has emerged yet," a spokesman for MirCorp, one of the companies sponsoring the proposed trip, said.
In May, Bass announced that he had been declared fit to go into space - but at that time, the space agency denied any contact with the singer.
They have now confirmed that talks are going on - but no contract has been signed.
"The talks could lead to one being signed, but so far there is no time frame for this," a spokesman for the agency, Rosaviakosmos, said.
Bass - who would become one of the youngest people ever to go into space - could travel on the next mission to the International Space Station, in October, MirCom said.
"If everything goes quickly and smoothly, there is still time for [Bass] to make the flight. Otherwise, he can take the flight next spring," the MirCom spokesman said.
Bass recently had a minor heart operation to rectify an irregular heartbeat in preparation for a mission.
'Confident'
If the deal was signed, he would follow in the footsteps of pioneering space tourists Dennis Tito and Mark Shuttleworth, who reportedly paid $20m (£14m) each for their trips to the space station.
Bass has previously said that he is "pretty confident" that the deal will be finalised.
He has said it was his "lifelong dream" to go into orbit after attending a space camp as a child.
The Russian space agency has kept one seat available in the three-person Soyuz spacecraft set to launch in the autumn.