It is very unlikely that Nick Heidfeld wil return in the Williams cockpit. It was expected that Heidfeld would test this week at Jerez, however Williams confirmed that Mark Webber and Antonio Pizzonia are going to run the test session. Nick Heidfeld’s last race for Williams was the GP of Turkey.
Nico Rosberg is also left out of the testing schedule, this makes it more likely that Antonio Pizzonia is going to drive the Grand-Prix of China en Japan for Williams.
Heidfeld already signed to swhitch to the BMW Formula 1 team for next year. It’s believed that is the reasion why Pizzonia replaces Heidfeld.