The 32-year-old Spaniard, who has been with the Banesto team all his career, has been rumoured to be on the point of announcing his retirement since losing to Denmark's Bjarne Riis in this year's Tour.
The Banesto team, financed by a Spanish bank, have signed 1995 world champion, Abraham Olano of Spain, but Indurain said after withdrawing from the Tour of Spain in September: "Some people have buried me too quickly."
Once, sponsored by the Spanish Blind Association, reportedly promised Indurain that their French rider Laurent Jalabert and Alex Zulle would help him in his attempt for a sixth Tour win.
Indurain was upset when Banesto refused to invite his personal doctor, Sabino Padilla, to join the team during this year's Tour de France after he took up a job as doctor to the Athletic Bilbao soccer club.
Indurain, who reportedly met Once team manager Manolo Saiz last week, paid for Padilla to join him in France.
However, Once might have difficulty fulfilling their promise as Zulle might have ambitions of his own to win the French classic.
The 28-year-old Swiss rider, runner-up to Indurain in the 1995 Tour de France, won the Tour of Spain and the world time-trial championship recently to make amends for a massively disappointing Tour de France.
He had originally decided to call it a day in order to concentrate on developing his cycle equipment business.
But he declared it would be premature to quit and put back his retirement until after the 1998 Commonwealth Games in Kuala Lumpur.
Obree has gradually been getting back to full fitness following his disappointing Olympics in Atlanta where he was far from his world record-breaking best due to a virus.
"It would be premature to retire and even though my business commitments may give me less time to train I could still compete effectively in track events on a scaled-down training schedule," he said.
Obree is still furious at the world governing body's decision to impose a second ban on him, this time because they find his straight-arm riding position unacceptable on "aesthetic grounds".