Williams have revealed that Robert Kubica had "another productive day" in testing as he strives for an incredible Formula One return next year.

The Polish driver has not raced in F1 since sustaining a serious arm injury in a rally accident in 2011, but Williams have offered him the chance to earn a seat.

Felipe Massa is keen to stay on as Lance Stroll's team-mate for another year, but Kubica and reserve driver Paul di Resta are also vying for a drive in 2018.

Kubica was behind the wheel of the 2014-spec FW36 on Tuesday, just as he was at Silverstone last week, and Williams declared that he had another positive day of testing at the Hungaroring.

Di Resta will get another chance to stake his claim on the track in Hungary on Wednesday.

Massa recently stated that he is unsure what Williams will learn from what has been billed as a testing 'shoot-out' for his seat between Kubica and Di Resta.