Former Formula 1 driver Karun Chandhok believes Robert Kubica had "plenty of opportunities" to prove himself worthy of a seat on the 2018 grid.

It was confirmed on Tuesday, that Sergey Sirotkin had been chosen by Williams to replace Felipe Massa, with the Pole earning the position of reserve and development driver for the upcoming season.

Having already tested both the 2012 and 2017 Renault during the summer before Carlos Sainz made the switch and later running the 2014 and 2017 Williams as he pushed for a much-anticipated return, Chandhok believes Kubica can't really complain.

"It's a shame, but I think they gave him plenty of opportunities to really prove that he deserves a seat in a meritocratic way," the Indian driver turned pundit said at the Autosport International last week, as Sirotkin had been widely expected to earn the Williams drive.

"I can't think of many other drivers who have had this many opportunities with two teams and I don't think you can say he hasn't had a fair chance to be evaluated."

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It is believed the data from the post-season test in Abu Dhabi last November showed the Russian as the slightly faster of the two drivers with Kubica also understood to be struggling with the Pirelli tyres. 

"The reality is teams can't hire drivers based on the past, they have to hire drivers based on their circumstances and their performance today," Chandhok added. "It's a shame for the sport and for Robert obviously that it's not worked out."

Fans didn't take the disappointment too well and many agree that Sirotkin's extra financial backing was decisive, offering around double that Kubica could manage.

"I think it's more down to the bank balance that he's missing out at the end of the day," technical analyst Gary Anderson commented.

"I believe in his talent. I don't think you can actually just jump into a Renault F1 car or a Williams F1 car for a one-day test as such and just drive the wheels off it.

"The long-run pace was there and you know the one-lap pace will come because you just need to have confidence in the car around you."