Sir Jackie Stewart has said that Lewis Hamilton is risking his long-term future by moving to Mercedes.
The three-time world champion believes that Mercedes could quit Formula 1 if they do not start to win.
Stewart told Autosport: "I think [Mercedes' team principal] Ross Brawn is a wonderful man. I think Daimler Benz is one of the greatest companies in the history of motorsport, but they have to win. The Silver Arrow has to win. And if they don't win, they get out.
"That's the risk. If for whatever reason, they do not win, it's a five-minute board meeting decision with a bunch of people on the board who are not passionate about motorsport.
"If you were looking at it in a conservative fashion, you'd say 'I've got to stick with McLaren because I know they're always going to be racers'. They will never be out of motor racing."
The 2008 world champion replaces Michael Schumacher at Mercedes from this year, following the German's second retirement from the sport.
