Robert Kubica OUT of running for 2018 seat as Williams prefer Sergey Sirotkin
Sergey Sirotkin impressed in testing but also comes with massive financial backing
Kubica had been given extensive testing time by Williams after initially returning to an F1 car earlier this year with Renault.
The Pole raced 76 times in F1 for BMW Sauber and latterly Renault between 2006 and 2010 before a massive rallying crash in 2011 left him with life-altering injuries.
Compound fractures to his leg, elbow and shoulder, a partial amputation of his forearm and damage to his wrist left competitive driving an unlikely future career for Kubica.
But he fought back to compete in rally-driving and Renault were seriously contemplating replacing Jolyon Palmer with him earlier this year.