'N Sync singer Lance Bass's hopes of joining a mission to the International Space Station in October could be dashed after he failed to meet a payment deadline.

Russia's space agency spokesman Sergei Gorbunov said there were a number of deadlines for the instalments to be paid, but that the first part had "already been delayed".

Bass is currently training for the mission in Star City, just outside Moscow, but reportedly owes them training fees, as well as missing the deadline for the mission payment.

"If Star City, where he has also not paid a large part of his training fees, decides to cut short his training, this would be enough to take him off the flight," said Mr Gorbunov.

If they do not pay up then, I don't know what will happen. We cannot wait forever

Sergei Gorbunov, mission spokesman

Bass is being sponsored by a consortium of major companies and Hollywood producer David Krieff, and has signed a preliminary contract for the mission.

However, he has yet to secure a deal guaranteeing him a seat on the Soyuz Craft.

Reports suggest that the singer's flight, which will cost around $20m (£12.7m), is still set for 28 October.

"His backers have sent us a letter asking us to set back the deadline to 9 August," Gorbunov said.

"If they do not pay up then, I don't know what will happen. Maybe we will follow their wishes and wait again."

Bass has been training for the mission in Moscow

"But we cannot wait forever."

Bass, 23, would be the third fare-paying tourist to blast into space aboard a Russian craft, following US millionaire Dennis Tito and South African businessman Mark Shuttleworth.

If he does join the mission, he will become the youngest person to visit space, replacing Soviet cosmonaut German Titov, who was 25 when he blasted off in 1961.

He has held the ambition since childhood, when he went to a space camp.

And he was recently declared both physically and mentally fit for the mission, following an operation to correct an irregular heartbeat.