Earlier, the Interfax news agency cited an unnamed official at Russia's cosmonaut training center as saying that Olsen, who has been at the center since April, was rejected for health reasons.

In a statement sent to The Associated Press, Space Adventures spokesman Robert Volmer said that recent medical evaluations raised concerns that Olsen "may have a medical condition that could potentially prevent him from participating as a cosmonaut in the Russian space program.

"At this point in time, there is no certainty that this potential condition will preclude Dr. Olsen from his orbital mission to the international space station."

Olsen hopes to blast off next spring aboard a Russian Soyuz space capsule for the space station in a US$20 million trip organized through Space Adventures.

All potential space tourists must train in mock-ups of the Soyuz and of the space station and undergo physical conditioning, scientific lessons and language training.

The world's only two space tourists were American Dennis Tito and South African Mark Shuttleworth.

U.S. pop star Lance Bass had hoped to be on a flight in 2002 and had also trained at Russia's cosmonaut center, but he was bumped from the crew after he failed to come up with fare.

Olsen, the founder of Sensors Unlimited, Inc., in Princeton, N.J., has said he hoped to carry out experiments in space.