Michael Schumacher has admitted his former protege and friend Sebastian Vettel might accept the "new challenge" of a Ferrari cockpit.
Felipe Massa's new contract for just 2013 has only intensified speculation that the Ferrari door for Red Bull's double world champion is wide open.
Some think the 25-year-old German has signed some sort of 2014 'option'.
Schumacher is quoted in Berlin by DPA news agency: "Seb speaks in high tones about Ferrari, but I don't know what the future holds."
Michael Schumacher, returning to retirement at the end of the year, is Ferrari's most famous and successful driver, having won five consecutive championships with the Italian marque.
Also as a two-time champion with a different team, Schumacher agreed to join the then-struggling Ferrari as a 26-year-old in 1996.
Referring to the Vettel rumours, Schumacher added: "At some point, it may be that he is looking for a new challenge too."