Williams will wait until the new year before making an announcement regarding its Formula 1 driver line-up for the 2018 season.
Williams holds the final vacant seat in F1 for next year, with Felipe Massa retiring at the last race of the 2017 season in Abu Dhabi at the end of November.
The Brazilian’s departure has opened up a seat alongside Lance Stroll for 2018, which looked poised to be taken by Robert Kubica, over seven years after he last raced in F1 before injuries sustained in a rally accident appeared to cut his career short.
Doubts emerged about Kubica’s comeback following a test with Williams in its 2017-spec car in Abu Dhabi after the final race of the season, leading to Russian youngster Sergey Sirotkin becoming the favorite.
Besides Kubica and Sirotkin, ditched Toro Rosso driver Daniil Kvyat is also an option, but Williams has now confirmed it will make no decision on its line-up until the new year.
Sirotkin first entered the frame in F1 in 2013 when he became a development driver at Sauber, with Russian backers SMP Racing pushing to get him a race seat for the following year.
Sirotkin missed out on a full-time role at the team, leading him to focus on racing in Formula Renault 3.5 for 2014 before spending two years in GP2, where he finished third in the standings in both seasons.
Renault struck an agreement to sign Sirotkin in a junior role in 2016, leading to a number of practice run-outs over the last two seasons, but he was passed over for a 2018 race seat when it signed Carlos Sainz Jr.
Williams emerged as an option for Sirotkin following a successful maiden test with the team in Abu Dhabi alongside Kubica, with talks now set to continue over the holiday period.
Sirotkin has not taken on a full-time race program this year, making just a single competitive appearance in the 24 Hours of Le Mans with SMP Racing in the LMP2 class.
Sirotkin has also been involved in the development of the team’s BR Engineering-designed LMP1 car for the 2018 FIA World Endurance Championship season, and is likely to secure a seat should he miss out on the role at Williams.