Robert Kubica has been trying to make a comeback to Formula 1 after his horrific injury in 2011, and he's been testing for Williams in recent weeks.
Kubica was actually considered the favorite to land the second spot with Williams, but Autosport has reported that Sergey Sirotkin is now the favorite over Kubica.
Williams hasn't made an official comment about who will join the team, and they will likely remain quiet until they are sure who they want to fill the spot.
The report from Autosport suggests that Sirotkin's testing data has been superior to any other driver who has tested for them, including Kubica and Paul di Resta, who has been a reserve for Williams.
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"Talks with the 22-year-old Russian, who has performed reserve duties for Renault this year, are now at an advanced stage," said Lawrence Barretto of Autosport.
"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."
If Sirotkin does land the spot, he will join Lance Stroll at Williams.
If Kubica did make it back to race full-time in F1, it would be a tremendous story. The fact that he's even in consideration given part of his right forearm was severed in a 2011 crash is already impressive enough.