Marc Gene will stand in for the injured Ralf Schumacher at this weekend's French Grand Prix.
Schumacher suffered cracked vertebrae in his back in a heavy accident two weeks ago at Indianapolis during the United States Grand Prix.
He is expected to be out of action for up to three months, casting into doubt whether he will ever again drive a Williams, with his current contract expiring at the end of the season.
The German's place this weekend at Magny-Cours will be taken by Gene, who has covered thousands of miles as Williams' test driver in recent seasons.
The Spaniard filled in for Schumacher last season in Italy after another heavy shunt for world champion Michael Schumacher's younger brother. Gene impressed on that occasion by finishing fifth.