Adrian Sutil is back in Formula 1 having signed as Williams official reserve driver for the 2015.
Although Williams already have a test driver in place in Susie Wolff, Pat Symonds revealed in the wake of Valtteri Bottas' absence in Australia that the Scot was not their reserve driver.
Symonds added that the team would be looking for a such a candidate immediately.
The former Sauber driver was left without a race-seat for this year's Championship after being dropped by the Swiss team in the wake of a dismal 2014 season.
Williams made the announcement on Thursday, stated that Sutil will spend time in the team's race simulator to ensure he is "fully accustomed to the Williams Mercedes FW37 controls and procedures" should he be required to race.
"I'm very proud to be a part of such a famous and great F1 team," said Sutil. "To work for Sir Frank Williams and his team means a lot to me.
"I would like to thank everyone at Williams for their belief in my qualities and the opportunity to work with such a successful and competitive outfit."
Meanwhile, Frank Williams, welcomed the German to the team.
"I'm delighted to have Adrian join our stable of drivers for the 2015 season. Adrian brings extensive racing experience, having competed 128 Formula One races during his career," he said.
"Having most recently raced during the 2014 season also gives him excellent knowledge of the current generation of race car and new Hybrid power units, which is invaluable for anyone needing to step into the cockpit in 2015.
"The fight for a top Constructors’ Championship position will be intense this season, therefore we have selected a driver with recent race experience and are confident that if the need arose, he would be a solid pair of hands to race the FW37 and assist our 2015 campaign."