The singer from the massively popular US boy band recently had a minor heart operation to rectify an irregular heartbeat in preparation for a mission.
But the situation was thrown into confusion on Wednesday, when Russian space agency officials said they had had no contact with the star or his entourage.
The 23-year-old wants to board the International Space Station on a Russian rocket later this year.
If the differences are resolved, he could 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.
"I'm pretty confident we will be able to pull this off. I know physically I can do this," Bass told a packed news conference in a Moscow hotel on Friday.
He told Reuters in an interview during his first trip to Moscow in March that it was his "life-long dream" to fly into orbit.
The next manned Russian rocket to the space station is likely to launch in September or October.
Flight training
Bass had expected to be officially certified fit at a ceremony on Wednesday after completing a series of physical and medical tests following the end of 'N Sync's latest tour.
He now hopes to start five or six months of flight training at the cosmonaut centre in Russia's Star City.
Bass will become one of the youngest people ever to go into space if he gets to fulfil his childhood ambitions, stemming from a visit to space camp.
The Russian space agency has kept one seat available in the three-person Soyuz spacecraft set to launch in the autumn.
A Russian cosmonaut will start training for the mission if it becomes clear that no space tourist will join the trip.
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