Spa-Francorchamps, Belgium - BMW-Sauber driver Nick Heidfeld on Saturday managed the fastest time in the free practise ahead of qualifying for Sunday's Belgian Formula One Grand Prix at Spa- Francorchamps.

The German clocked 1 minute 45.388 seconds for a 7.004-kilometre lap, just 0.074 seconds faster than Toyota's Jarno Trulli of Italy, with Adrian Sutil in a Force India third.

Overall leader Jenson Button in a Brawn GP had the tenth-fastest time.

Ferrari's Luca Badoer, replacing the injured Felipe Massa, again struggled, finishing second-last of all the timed drivers.

Valencia, Spain  - German driver Nick Heidfeld remains confident of continuing in Formula One despite the withdrawal of BMW at the end of the season.

Heidfeld, 32, told German Press Agency dpa he had already been in talks with other teams before BMW's decision, although the announcement at the end of last month took him by surprise.

With seven races left of the season with BMW Sauber - beginning with Sunday's European Grand Prix in Valencia - Heidfeld admitted he was now in the shop window in seeking a new contract elsewhere.

Istanbul - Nick Heidfeld is uncertain where his future lies in Formula One as his BMW-Sauber team continues to struggle for points this season.

"As always, at the appropriate time I will consider the relevant options that promise the most success in the future," the 32-year-old told the German Press Agency dpa ahead of Sunday's Turkish Grand Prix in Istanbul.

Heidfeld's comments come on the back of growing speculation that BMW intends pulling out of the sport at the end of this season.