Why is Mercedes' 'exceptional' talent on the F1 scrapheap?

When Pascal Wehrlein signed for Sauber ahead of last season, there was a feeling it was an underwhelming move for the Mercedes protege.

He had delivered in every category, winning the ADAC Formel Masters title, becoming a European Formula 3 race winner and earning the distinction of being the DTM's youngest champion.

Wehrlein then performed strongly in what was the slowest car on the grid in 2016, dragging the Manor into Q2 four times in the final nine races and scoring its only point in Austria.

But fast forward 12 months and how grateful Wehrlein would be to have a Sauber contract in his back pocket again. With Williams set to sign Sergey Sirotkin for next season to complete the 2018 field, Wehrlein will not have a F1 race seat this year.

It is a frustrating scenario for Wehrlein, who was considered as a candidate to drive for the works Mercedes team when Nico Rosberg departed, though Valtteri Bottas got the nod given his experience. So how has a driver that was heralded as a future star found himself facing the prospect of his F1 career ending aged just 23?

Statistically, Wehrlein outperformed Sauber team-mate Marcus Ericsson. He scored all five of the team's points and won the qualifying head-to-head 11-7. But he was expected to comfortably beat Ericsson and that didn't happen. The qualifying gap between the two was the smallest of any team pairing on the grid.

Speak to members of the Sauber team and there will be those who tell you Wehrlein was the stronger of the two over the course of the season. They will tell you he had a series of engine problems and that circumstances meant he was not able to show his true potential.

He was also at the mercy of goings-on that were beyond his control. Ferrari wanted to increase its relationship with Sauber, which ultimately extended to bringing back the Alfa Romeo brand, giving its protege Charles Leclerc his F1 debut and a strong technical partnership that includes the latest specification engine.

With the team's Swedish backers continuing to throw their support behind Ericsson, Wehrlein simply got shuffled out of the equation. There was nothing he could do.

Sauber was the worst team of the year in 2017. To have your first two years in F1 with the two worst teams is not ideal. There is a limit to what you can do. Sauber's form tailed off as the season went on and Wehrlein believed his good drives - he ended the year with three successive 14th places - went unnoticed.

Ocon's form has pushed him to the top of the list that Mercedes will consult when considering who to promote

"In terms of result, [Barcelona] was the best race of the year but probably in the second half of the season I had better races, but you couldn't see it," said Wehrlein.

"Even if we had a good race in the second half of the season you couldn't see it because the gap was just too big - for example, in Suzuka, I was lapped by the second-last guys.

"I'm quite happy in the end with five points. Not all of the races have been good as I wished but in general we did what we could do.

"I was always giving my best, and I think that's the most important thing that you can say about yourself. When an opportunity was there, we took it."

Other factors, again out of his control, have hurt him, too. Fellow Mercedes junior Esteban Ocon excelled in his debut season with Force India.

Ocon scored points in all but two races, pushed experienced team-mate Sergio Perez hard all season and you could argue he was the stronger of the two overall, even if the points don't quite reflect that. He was even voted the fifth best driver of 2017 by the team principals in Autosport's secret poll.

It's that kind of form that has pushed him to the top of the list that Mercedes will consult when considering who to promote to the works team in the future.

Then George Russell shone when he drove for Force India in Friday practice sessions in Brazil and Abu Dhabi. The team was so impressed it is pushing for him to have a role this season, with the details still being ironed out.

With Wehrlein on the sidelines, mostly likely in a Mercedes reserve role this year alongside a drive in another series that has yet to be confirmed, he has dropped to third.

The fact Ocon has performed so well at Force India, having been selected over Wehrlein by the team's senior management based on a series of factors, will particularly hurt. That the same team has now spoken so highly of Russell will enhance that pain.

It is certainly not all over for Wehrlein. Mercedes team principal Toto Wolff has publicly backed the German and insisted he will stay part of the family.

"He deserves to be in Formula 1, he is a very good driver," said Wolff of Wehrlein. "On track his performance was exceptional, and for many other reasons that go much beyond the driving the doors haven't opened like we would have hoped.

"He has the potential of being a successful Formula 1 driver. He's definitely going to be on our team [this year]. [It is unclear] whether or not he actively participates in a racing series other than Formula 1. He will definitely remain part of our squad."

There is small comfort to take there, but Mercedes will be hedging its bets.

By next year, if Russell impresses in Formula 2 this season, while also further endearing himself to Force India, he will be in a strong position to get a race seat somewhere on the F1 grid.

But 2019 will be a very open driver market, with seats available at Mercedes, Ferrari, Red Bull, Force India, McLaren, Renault, Toro Rosso, Haas, Sauber and possibly Williams. Wehrlein, with his experience, would be in contention - it's just he's further down the list now.

For now, Wehrlein's future is no longer in his hands

Wehrlein has grown stronger this year in what has been a particularly challenging environment. It is difficult for a driver to show his true potential when there are technical issues. It is even harder when he is facing a driver that has financial support from the team's backers.

Sauber insiders suggest he made a good impression in terms of work ethic, quality of feedback and personality. The improvement of the latter is of particular importance.

Before joining Sauber, there was the perception among some in the paddock that Wehrlein was difficult to get along with. He missed out on the Force India seat not because of his on-track performances, but how it was believed he would have integrated into the team.

Manor refuted any claims that Wehrlein was difficult to get on with and Sauber has now backed up that view. There is a feeling he will protect and look after those around him and is a great driver to work with. If that can filter through, that will bode well for his future.

But for now, his future is no longer in his hands.

He must continue to work hard and deliver on the tasks Mercedes gives him this season and hope that he emerges as a stronger candidate than Ocon or Russell when decisions need to be made for the future.

A second year out of an F1 race seat will almost certainly end his career at the highest level.