Sergey Sirotkin has emerged as the favourite to drive for Williams in 2018, with Robert Kubica no longer in the frame, Autosport has learned.
Williams has spent the last week evaluating data gathering from the Abu Dhabi Pirelli test at Yas Marina, where it ran Sirotkin and Kubica.
Kubica had been favourite to make a sensational return to F1, with the team impressed by his feedback and the way he fitted into the team and built up strong relationships.
However, it has emerged that based purely on performance, data suggests Sirotkin is the stronger candidate.
Williams has insisted throughout the process that its decision on the driver to partner Lance Stroll next season will be based on performance.
Talks with the 22-year-old Russian, who has performed reserve duties for Renault this year, are now at an advanced stage.
However, it is believed there are several details still to be ironed out before the final contract is signed.
It is believed Sirotkin brings substantial backing with him - understood to be in the region of £15million - from Russia's SMP Racing, which was founded by Boris Rotenberg, who controls SMP Bank.
Should the deal fall through, former Toro Rosso and Red Bull driver Daniil Kvyat is believed to be the back-up option.
However, it is believed Kubica is no longer in contention for the race seat, ending his hopes of returning to the grid for the first time since 2010.
Autosport understands Williams reserve Paul di Resta, who stood in for the injured Felipe Massa in Hungary this year, is also out of the running.
Williams is remaining tight-lipped and not making any official comment regarding its 2018 driver line-up.
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