Rumours suggesting Michael Schumacher could return to Formula One next season have intensified after Ferrari said they would not stop the German racing with another team.

The seven-time world champion has been linked with Mercedes, who have taken over world champions Brawn and already signed driver Nico Rosberg for 2010.

It is believed that Mercedes are keen on having an all-German line-up next year.

"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 chief Luca di 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 is currently an ambassador, consultant and test driver for the Ferrari's road cars.

German newspaper Bild recently reported that 40-year-old Schumacher has already agreed a deal, thought to be worth 7million euros, with Mercedes.