Esteban Ocon looks increasingly likely to sit out the 2019 season.
Toto Wolff, the Mercedes boss, said the Frenchman's chances of securing the second place at Williams for 2019 are "minimal".
"Over the past two months the situation has not changed," he said. "We are already thinking about 2020.
"Esteban will help us with the Mercedes car, and then we'll see what awaits him."
Mercedes successfully placed its other development driver, George Russell, at Williams for 2019. But Wolff said it is a "completely different situation" for Ocon, who has lost his seat at Force India.
"Perhaps it will be good for him to miss a year and return to a competitive car," he said.
The big rumour is that the 'competitive car' could be Valtteri Bottas' seat at Mercedes.
The Finn has struggled, particularly in the second half of 2018.
"I have lost a lot of points this year and in the second half I never finished ahead of Lewis (Hamilton)," Bottas acknowledged in Mexico.
"But I don't think I am really 130 points behind him. The difference between us is much smaller. I know it and so does the team," he added.
