Pirelli has called off Ken Block's test in the 2009 Toyota.
The 43-year-old American was scheduled to drive the car this week at Monza, as F1's official tyre supplier tests privately at the famous high-speed Italian grand prix venue.
Block, a world rally driver, is arguably most famous for his online gymkhana stunt videos, but his large size - 6 foot 2 and 84 kilograms - has proved problematic for the 2009 Toyota.
The car, designed originally for the diminutive Jarno Trulli and Timo Glock and tested this week by Lucas di Grassi, is too small to accomodate Block, Pirelli's motor sport director Paul Hembery said on Thursday.
"Ken is too big," said the Briton. "We are looking at running him in another car."