Mercedes has been working hard to persuade Williams to take Wehrlein, with the obvious possibility of including a commercial element in any deal, such as a discount on the team's power unit costs.

However, Wolff says that Kubica, who will test the FW40 in Abu Dhabi next week, deserves the opportunity to make a comeback.

"I think it has been clearly said that Williams's priority is Robert," Wolff told Motorsport.com. "Robert from my point of view deserves the chance in the Williams, and it's out of Pascal's hands.

"There is still a tiny possibility if Robert doesn't do well, but none of us wishes him to not do well. All of us are actually cheering for him.

"I'm in two minds, because I think for F1, for Robert and for Williams it will be great if he performs, and on the other side it looks like it's Pascal's last chance, and he's our junior. Let's see how things develop."

Wolff said there's a limit to what Mercedes can do to push the case for one of its drivers.

"I don't think as a team we should be forcing Pascal into one of our customers, because it's very much at the core of F1 that you have to respect that the team always tries to get the best available driver, and I respect Williams and Force India taking their own decisions on their drivers. I wouldn't want to interfere."

Wolff acknowledged that Wehrlein could become third driver at Mercedes in 2018, but suggested that a racing programme would be preferable.

"There could be a role, but I don't think that's enough."

Wehrlein has been linked with a return to the DTM, where he won the 2015 title, and the departure of Robert Wickens to IndyCar has opened up a seat.

However, Wolff says no decision has been made about other options.

"We have concentrated on Plan A, and we'll see how it goes, and if Plan A doesn't work then you need to look at all the other options. Nothing is set in stone.

"I'm not sure DTM is the logical place, because he's won it. I think it's about evaluating whether you want to give up on a single-seater career or not.

"In the end it's about him performing in the car. Pascal has a lot to bring, and people know that. Whether you put him in an IndyCar or Super Formula car or anything else, he will perform very strongly."

Wehrlein said that he has been actively pushing Wolff for news, rather than just waiting to see what might happen.

"I always like to be proactive and be involved in everything, and know about the talks, discussions and everything. I like to be involved. So I'm not saying OK, they will do it for me, I don't have to worry.

"I don't like that too much, I'm always proactive – I guess I'm annoying Toto on his telephone! You know the paddock is so small, you're in contact with everyone."

Wehrlein insisted that missing out on a 2018 seat would not signal the end of his F1 career: "No, I don't think so. I won't retire!"