Williams will run Sergey Sirotkin next week in Abu Dhabi at the team's post-race Pirelli test where Robert Kubica will also drive the team's 2017-spec car.
The 22-year-old Russia, who ran this year in four Friday free practice sessions for Renault, will take to the track in the team's FW40 on the second day of the two-day test while Kubica will run on the morning of the first day, with Lance Stroll taking over in the afternoon.
The Polish driver is the lead contender for Williams' second seat alongside Lance Stroll next year, with Paul di Resta, Pascal Wehrlein and Dany Kvyat also under consideration for the drive.
It's unknown at this stage if Sirotkin's presence behind the wheel of the Williams is a one-off opportunity or if the Russian hopeful is a last-minute addition to the team's short-list for 2018.
German broadcaster RTL GP announced earlier this week that Kubica had signed a two-year contract with Williams, but the British team denied it had concluded a deal with the Pole.
Williams said in a statement yesterday that "conversations are ongoing" with Kubica, with no announcement planned for this weekend.