Schumacher, 41 in January, won five successive F1 titles from 2000-04
Ferrari have insisted they will not prevent Michael Schumacher making a Formula 1 return with another team.
The seven-time world champion has been a consultant for Ferrari since retiring in 2006 and said recently he would stay in the role for another three years.
But Ferrari chief Luca di Montezemolo says his position is "not binding".
Schumacher, 40, has been linked with a move to Mercedes, who have taken over world champions Brawn and already signed driver Nico Rosberg for 2010.
Schumacher was on the brink of a racing return with Ferrari in August to deputise for the injured Felipe Massa.
Those plans were abandoned following medical checks on a neck injury the German suffered in a motorcycle accident earlier this year.
With that neck problem now understood to be fully healed, Schumacher is thought to be close to completing a sensational return to the sport with German giants Mercedes.
"If he takes another road, our agreement will no longer be valid. You can't work with a competitor and with us at the same time," said Ferrari president Montezemolo.
"I still haven't spoken to him about it. He is only a dear friend, not a team member. He is a consultant for our road cars."
Schumacher agreed a new role with Ferrari over the summer, cutting his links with the F1 team to become an ambassador, consultant and test driver for the company's road cars.
Now Mercedes are understood to want him to launch their return to F1 following the takeover of Brawn.
Countryman Rosberg, 24, has already been signed up, but the team's second driver has yet to be confirmed, although they have also been linked with Nick Heidfeld.
Rosberg excited by Schumacher rumours
"I hope that my team-mate will be sorted out pretty soon and at the moment the rumours are very strong for Michael Schumacher," said Rosberg, who drove for Williams between 2006 and 2009.
"I have no idea if it is true or not but obviously if he would join that would be an absolutely fantastic move."
German newspaper Bild reported that Schumacher, who turns 41 in January, had already agreed a deal, thought to be worth 7m euros, with Mercedes in principle.
Should he return, Schumacher would go head-to-head with fellow world champions Jenson Button, Lewis Hamilton and Fernando Alonso.
Button, who won the 2009 title with Brawn, will drive for McLaren in 2010, alongside fellow Briton and 2008 champion Hamilton.
Alonso, champion in 2005 and 2006, will spearhead Ferrari's challenge following his move from Renault.
Button has already told BBC Sport that Ferrari, Mercedes and Red Bull are the teams most likely to trouble McLaren next season.