Williams has pushed back to next month the announcement of its 2018 driver line-up, but Sergey Sirotkin remains the team's most likely choice.
The Russian's surprise presence with Williams and subsequent good performance at last month's post-season Abu Dhabi tyre test has put the 22-year-old in pole position for a drive also targeted by Robert Kubica.
Based on performance alone, the Pole was apparently told by Williams' management that he was no longer a contender for the 2018 seat alongside Lance Stroll.
But Kubica's father, Arthur Kubica, insists his son and his management team are still fighting for a deal with the Grove-based outfit.
Reports indicate that Williams is in the process of finalising Sirotkin's contract, with both parties now focused on minor details and the preparation of a formal announcement scheduled for after the new year.