Heidfeld no cause for concern - Williams

Williams say they have no worries about Nick Heidfeld being fit for next Sunday's San Marino Grand Prix after the German Formula One driver pulled out of testing with back pains on Thursday.

"We have no concerns whatsoever," said a spokesman for the BMW-powered team.

"It's fairly minor. He had a back twinge early in the day, felt uncomfortable after a few laps and got out of the car."

The German, who finished third in last month's Malaysian Grand Prix and had been testing at the Le Castellet circuit in southern France, returned home for physiotherapy.

Heidfeld's Australian team-mate Mark Webber started the season with a fractured rib that he suffered in testing in Spain in February.

Both can expect a jarring time at the anti-clockwise Imola circuit, where drivers have to attack the kerbs aggressively to get a good lap time.