In August 2010, with Heidfeld not yet having driven the Mercedes MGP W01 car, the team released him from his contract so that he could become the Pirelli tyre company's test driver. Heidfeld tested a Toyota TF109 car fitted with Pirelli tyres on a number of occasions in 2010, ahead of the firm's replacement of Bridgestone as the sport's sole tyre supplier in 2011. Heidfeld completed three tests for Pirelli in Mugello, Paul Ricard and Jerez before being released from his duties to join Sauber, with his place being taken by Romain Grosjean.
In September 2010, Heidfeld returned to the Formula One grid, replacing Pedro de la Rosa at the Sauber team for the remainder of the 2010 season. This marked his third spell with them. On 4 October 2010, Sauber confirmed their driver line-up for 2011 as Kamui Kobayashi and Sergio Pérez, seemingly leaving Heidfeld without a drive for 2011, before replacing Robert Kubica at Renault, who was injured in a rally accident on 6 February 2011.