Grosjean replacing Heidfeld as Pirelli tester
Because Heidfeld has signed to return to racing with Sauber in Singapore and beyond, the Italian marque said the German will no longer work with F1's 2011 tire supplier "to avoid favoring any individual team".
The 33-year-old's last outing with Pirelli was this week at Jerez over two days.
And the 2011-2013 official supplier's next outing will be at Monza next week, with former Renault driver Grosjean at the wheel of the Toyota.
"He's packed a lot of experience into a short space of time, including all our GP3 tire development, so I'm sure he'll be able to give us some very useful feedback," said Pirelli's motor sport director Paul Hembery.
Swiss-born Frenchman Grosjean, 24, contested 7 grands prix with Renault last year, and most recently has been replacing injured GP2 driver Ho-Pin Tung.