The WilliamsF1 team would return to testing, this time at the Jerez circuit. The team would only use one driver on the day as they continued to test the interim FW28 powered by Toyota. For Rosberg this would be his first run with the Toyota engine. The session would get under way with a damp track from overnight rain. But the track would dry during the day.

Nico would further test Bridgestone's new 2007 tyres as well as running with the teams 2007 gearbox. He would finish the day in tenth place with a time of 1m:20.961. For the German the day would be spent getting use to the new setup of the car.

In an interview for news agency Sport-Informations-Dienst Nico said that he thought the switch to Toyota was not one that would see them gain a huge performance advantage. He said: "It will surely be a good engine, and reliable, but I do not believe that it is a huge jump over the Cosworth. "However, we had to look elsewhere."

WilliamsF1 Test Team Manager Mike Condliffe commented on the first days testing by saying: “Today was Nico's first outing in the interim FW28B with the Toyota engine, next year’s gearbox and the 2007-spec Bridgestone tyres so he spent some time adjusting to the balance of the car. Once Nico had acclimatised, he tested various brake balance positions and some traction control options. The session started out on a wet track, but the track surface eventually dried out before lunch.”