Michael Schumacher is open to the possibility of continuing his Formula 1 comeback beyond his current three-year deal with Mercedes.
The seven-time World Champion has been signed through to the end of 2012, by which time he will be 43 years old. But he says there is no guarantee that he will stop racing at that point.
"The good thing is that Mercedes believes in me and is giving me the chance for three years to have success," said Schumacher in an interview with German newspaper Bild. "But it does not mean it has to end after three years."
Schumacher said his excitement over his return was so great he could easily see himself committing for longer than his present contract.
"I thought about everything very carefully: 'Am I just spontaneously high or will my enthusiasm last?'" he said. "I have been excited for quite some time and can imagine doing this for a few years."
Mercedes GP boss Ross Brawn said earlier today that the team knew it could not rely on Schumacher too far into the future so was keen to develop his teammate Nico Rosberg as a championship challenger, too.
"Michael has come out of retirement but we have to accept that there will come a day when he has to stop forever and then we will have Nico," Brawn told the official F1 website.
The next major step in Schumacher's comeback takes place next Monday, when he tests the 2010 Mercedes F1 car for the first time.