Robert Kubica and Paul di Resta are set to take part in two one-day tests with Williams to evaluate both drivers over a possible 2018 seat with the team.
The pair are understood to be in direct competition with Felipe Massa over his seat at Williams, with the Grove-based outfit keen to assess which driver of the three should partner Lance Stroll next year.
Williams plans to run both Kubica and di Resta in a one day test at Silverstone on October 11 in a 2014-spec F1 car, before a further test is carried out at the Hungaroring a few days later on October 18.
A potential return to the sport for Kubica has been one of the stories of the 2017 season, after the Pole completed a series of tests with Renault earlier this year, culminating in a full day in the team's 2017 challenger in the post-Hungarian Grand Prix test.
His chances of making a remarkable return to the sport took a hit when Renault announced it had signed Carlos Sainz as Jolyon Palmer's replacement for next season.
Kubica recently joined forces with reigning world champion and former Williams driver Nico Rosberg -- who set off the initial 2017 driver market chain reaction by retiring days after winning his maiden title -- in a managerial-based tie-up to boost his chances of an F1 return.
Massa is open to extending his four-year stint at the team into a fifth season, with Williams grateful the Brazilian reversed his decision to retire at the end of 2016 to return as Mercedes-bound Valtteri Bottas' replacement.
Di Resta recently acted as a last-minute replacement for Massa when he fell ill during the Hungarian Grand Prix and impressed to put himself in contention for a drive next year. The Scot, who had not raced in F1 since 2013, qualified just 0.7s behind Stroll despite having never driven Williams' 2017 challenger before qualifying.
At last weekend's Malaysian Grand Prix, Toto Wolff suggested that Mercedes junior Pascal Wehrlein is also in the frame with his options for 2018 becoming increasingly limited following Ferrari's renewed engine deal with Sauber.
However, such a move for the 22-year-old appears unlikely, as Williams requires one of its drivers to be over the age of 25 as part of its agreement with title sponsor and alcohol brand Martini.