The Australian’s current Formula 1 deal with Red Bull includes a contract with its title backer Infiniti, Nissan’s luxury brand, which does not run out until the end of this year.

That could prevent Webber, whose recruitment by Porsche for 2014 was announced last month, from joining the test programme with the new Porsche petrol-powered LMP1 hybrid until January 1.

A spokesman for Porsche said: “We would like him to start testing in November or December [after the end of the F1 season], but we don’t know if that is going to be possible.

“We do know that he will only be available for public relations duties from January 1.”