Ferrari driver Sebastian Vettel has questioned why the timing of Robert Kubica's decision to attempt a full return to Formula 1 with Williams in 2018, seven years after his serious rally crash.

The Pole initially started his efforts at a comeback with Renault earlier this year, testing both the 2012 and 2017 cars but after the French manufacturer signed Carlos Sainz, attention switched to Williams with the seat held previously by Felipe Massa the last available for next season.

So far, Kubica has completed four appearances, with his most recent coming at the post-season test in Abu Dhabi last week, but while understanding of the 32-year-old's desire to get back behind the wheel, Vettel wonders what took him so long.

“I think it’s very tragic what happened to him back then, he was considered a future champion," the German commented. “However, I do not understand why he is now pushing for a comeback. Why did he not do this earlier?"

The four-time world champion, who briefly worked with Robert at BMW a decade ago, also seemed to suggest Williams should look to the next generation when making their decision, despite already having the youngest driver on the grid in Lance Stroll.

“For him, it would certainly be a nice story, [but] on the other hand, it would be a pity for younger drivers, from whom he would take away a race-seat,” Vettel said.

The Grove team has made it clear they are considering all options, including names like Pascal Wehrlein, Daniil Kvyat and potential Sergey Sirotkin, who also drove for them at Yas Marina, but insist they will not rush into a choice.