Pascal Wehrlein has been confirmed as Mercedes' official reserve driver for the 2018 Formula 1 season.
It fulfils a promise made by the team to keep Wehrlein part of the Silver Arrows family, after he lost his Sauber race seat to Charles Leclerc over the winter.
Mercedes had hinted last month that it would make the 23-year-old its test driver, after failing to find him a new full-time F1 race seat.
"With Pascal we couldn't find the right solution," said Mercedes boss Toto Wolff. "But he's our reserve.
"We will see which options open up," Wolff added.
However Wehrlein will not be present at every Grand Prix because of his previously announced return to DTM. This year's Norisring and Misano rounds clash with the French and Belgian Grand Prix races.
On those occasions, Mercedes junior George Russell will be on standby in case Lewis Hamilton or Valtteri Bottas have to drop out.
The reigning GP3 champion will be at both races anyway, as he is taking part in this year's Formula 2 championship.
"We will see how George is going to go in F2," commented Wolff. "He does a brilliant job for us in the simulator. He has met our expectations in winning the GP3 title."
Russell had been hoping for an official reserve role at Force India this season. He had made two free practice appearances with the team in 2017. However, Nicolas Latifi has since been named as the team's reserve and test driver.
"Force India is very impressed by him," Wolff insisted. "F2 is the next step. We're keen to see how he's going to perform."
Speaking at Silverstone during the launch of the Mercedes' 2018 car, Wolff said tha team was working to expand its pool of driver talent.
"We are looking far into the future," Wolff revealed. "We have for the first time started to look into karting
"There is an exceptional young kid called Andrea Antonelli, barely 11 years old," he added. "It's just very enjoyable to go back to the grassroots of motor racing and follow these kids developing.
"Who knows, maybe in six or seven years, [today's] 10 or 11-year-old will be the next Lewis!"