The Russian backers and sponsors of Sergey Sirotkin have insisted that it was their decision to take the driver out of contention of the second Williams seat for 2019, saying they had no plans to return due to the underperformance of the team this season.
Sirotkin is dead last in the driver rankings for 2018, having picked up a solitary point in his debut F1 campaign, with Williams also languishing near the bottom of the constructors' championship.
Speculation mounted that the team would be replacing the Russian for 2019, and it was confirmed on Thursday morning that Robert Kubica would partner George Russell for Williams, with Sirotkin being left out.
Sirotkin's sponsors, however, said they didn't want the seat anyway.
"We took the decision not to continue participating in the Formula 1 world championship in the joint project with the Williams Martini Racing team," SNP founder Boris Rotenberg said.
"We were unpleasantly surprised by the team's performance level at the start of the season, and the car's development rate also turned out to be not high enough."