Sir Jackie Stewart is concerned that Lewis Hamilton is getting complacent in his bid for a fourth world title, after being overtaken by Nico Rosberg in the drivers' standings.
Hamilton had another difficult weekend in Singapore as his Mercedes team-mate stormed to a third straight Grand Prix win, putting himself eight points clear of the British driver with six races of the season to go.
He had been 19 points clear at the summer break, but Rosberg has stormed back since then to regain the momentum in what has been a topsy-turvy battle between the pair this year.
"Maybe you can bottom out," said Stewart. "That can happen through consistent success because when you have consistent success everything can seem so easy.
"Suddenly things can go less well - you overdrive, you are not on the ball, or you live a life that distracts you in one way or another.
"If you are at the top in any line of work, you can get carried away with success. You think you can get away with things. Then someone else comes along and drives better or more consistently."
Stewart, who is Britain's only other three-time F1 champion, said it was the fear that always drove him on in his own pursuit of glory.
"I was always frightened of being beaten," he said. "I always thought there could be someone out there better than me or who might have a better car. So I always worked on that basis. I could never sit back and relax."
Don't miss the F1 Report for all the reaction and analysis from the Singapore GP. F1 technical expert Craig Scarborough joins Natalie Pinkham and Marc Priestley in the studio at 8:30pm on Wednesday on Sky Sports F1.