Ken Block's test in a Formula 1 car has had to be postponed by Pirelli

The WRC driver, who is famous for his Gymkhana videos, had hoped to run at Pirelli's August test at Monza in its updated 2009 Toyota test car.

However, during a seat fitting at Toyota's Cologne headquarters, it was found that Block's legs were too long for him to be able to fit in the car.

Pirelli had hoped to be able to find an alternative chassis for Block, but so far its hunt has not been successful - which is why the August run has had to be called off.

Paul Hembery, Pirelli's director of motorsport, told AUTOSPORT: "We can't find a car big enough.

"The test has had to be delayed until we find a suitable vehicle. We're confident we can do it, but we haven't yet found the right car. And when we have found the right car, then we can't find the people to run it - because there are no longer any test teams and very few have running old F1 cars.

"To be honest, it's been a bit of a challenge - but we will make it happen."

Block told AUTOSPORT last month that he was overjoyed at Pirelli's plan to give him a chance in F1 machinery.

"I never imagined that something like this would even be available," he said. "But Pirelli saw the idea of doing something unique and different with me. They have been a great partner with me for everything I have been doing, so it is just something that for me is a dream come true.

"I have so little experience in open wheel asphalt, so it will be a huge learning experience for me."