Robert Kubica has completed the first of two days testing a 2014-spec Williams as part of the team's evaluation of his potential for a race seat next year.
Kubica has not raced in F1 since a 2011 rallying crash left him with severe injuries to his right arm. The Pole has returned to contention this year and was given a series of tests by Renault, culminating in a day behind the wheel of this year's car at the post-Hungarian Grand Prix test in Budapest.
Though Renault has since signed Carlos Sainz on a loan deal for next year, Kubica's attentions have now turned to Felipe Massa's seat at Williams. Massa's future has not been confirmed for next season and earlier this month the team confirmed plans to test Kubica and Paul di Resta to assess its options for next season.
Kubica completed day one at Silverstone on Wednesday, though Williams has not released any information on the session other than it being a "successful day". The Polish driver was at the wheel of the team's FW36 car used extensively by the driver he could partner in 2018, Canadian teenager Lance Stroll, in private tests this year.
Kubica recently enlisted the services of reigning world champion Nico Rosberg as his manager. Though there are lingering questions about Kubica's physical limitations, Rosberg has no doubts he is capable of returning.
"He [Kubica] is being evaluated amongst other drivers and I'm optimistic," Rosberg told Sky Sports F1 during the Japanese Grand Prix. "It is about getting to know each other and if it fits well it will be absolutely awesome to see Kubica back on the grid and in F1.
"Williams want to take the fastest possible driver out there and this guy is seriously impressive with unbelievable speed so that is why he is being evaluated."
Next week, Williams plans to test both Kubica and Di Resta on alternate days at Budapest's Hungaroring. Kubica was the star of the two-day test at circuit at the start of the summer break, with a large Polish contingent turning out to watch him drive.
Williams reserve driver Di Resta also drove a 2017 F1 car at the Hungaroring, deputising at for the unwell Massa at short notice ahead of qualifying and continuing through to the Hungarian Grand Prix itself. Given his short preparation time Di Resta made an impressive appearance and is believed to have been pushing for a full-time return ever since.
With both drivers having recent experience at the circuit, those tests are likely to give the team its best indication of the readiness of either driver.
With Fernando Alonso expected to re-sign with McLaren and Sauber likely to give newly-crowned Formula 2 champion and Ferrari junior Charles Leclerc a drive, Williams holds the last seat with a genuine question-mark for next season. While Kubica and Di Resta are being evaluated, Massa is also hopeful of being retained for another season alongside Stroll.