Ross Brawn says the true test of Sebastian Vettel's class will come when he is presented with a slower car than that of his rivals.

After Vettel secured back-to-back titles in Japan to become the youngest ever double world champion there has been some debate as to where he ranks among the greats of the sport. Brawn - who helped Michael Schumacher turn Ferrari in to a dominant force in the early 2000s - said that the next challenge would be to display an ability to replicate Schumacher and turn an uncompetitive team in to title challengers.

"For Sebastian, what will come now, which will be an interesting phase of his career, will be when he has not got the best car," Brawn is quoted by Autosport. "I think you have a fantastic driver in the best car, and that combination is unbeatable. It will be interesting to see Sebastian's role, Sebastian's influence, Sebastian's position when perhaps he does not have the best car, he has to make it the best car, and has to create the best car."

Brawn said that the move will come in the future when Vettel finds himself in need of a fresh challenge.

"That will be another chapter of Sebastian Vettel when it comes - and it will come. Perhaps he will make it happen himself, because he will go to another team as he wants them to be successful. And the challenge for Sebastian will be exactly the same as it was for Michael, that you have won two world championships, so what is next? What is the new challenge for me? What is the motivation?

"For Michael the motivation was to go to Ferrari and make that successful. I am sure Sebastian will look at that because everybody thinks Sebastian is doing a great job, but the Red Bull is a fantastic car. His ambition may take him a different direction, who knows?"

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