Mercedes would promote "one of our test drivers" to the race cockpit should regulars Michael Schumacher or Nico Rosberg be unable to drive in 2011.
Sergio Perez's recovery from his Monaco qualifying crash raised an interesting question, after Sauber's official reserve driver Esteban Gutierrez was overlooked for the Montreal seat.
Instead, McLaren's Pedro de la Rosa got the nod, while at Mercedes GP for instance it is not believed an official reserve has been nominated at all.
Asked by Auto Motor und Sport this week who is first in line for the Mercedes seats, motor racing vice president Norbert Haug answered: "One of our test drivers."
It appears he is referring to GP2 driver and Briton Sam Bird, and the McLaren-linked Gary Paffett, who has just signed a multi-year contract to keep racing with Mercedes in DTM.