Former Williams reserve driver Paul di Resta believes the team's driver line-up choice for the 2018 Formula 1 season is "a risky decision."

Di Resta carried out one day of a two-day test in 2014 machinery at the Hungaroring last summer, with Robert Kubica driving on the other day as Williams evaluated the Pole's potential to race again after injury. Kubica then got a chance to test the 2017 car in the Abu Dhabi tire test for Pirelli in November and had appeared a front-runner for the vacant race seat before Sergey Sirotkin was named as Lance Stroll's teammate.

Having felt he had a strong change of securing the seat himself, di Resta says Williams has taken a risk based on the level of competition it will face this season.

"I was very happy with the test I did [alongside Kubica in Hungary]," di Resta told RACER. "Exceptionally happy with the test I did. I had one of those days in a car that you couldn't ask for any better, and I feel that I delivered to the best of my potential, which they can see.

"It's a risky decision, the driver line-up, in the experience the guys have got. Obviously Lance has got a year under his belt, Sirotkin coming in... The key things for me is already you've got McLaren who are a key championship contender and Renault as a constructor should be able to beat somebody like Williams. Where does that fall within where you are in keeping the momentum?

"Obviously as the years go on, the experience of having a Mercedes engine diminishes a bit, so they've got a tough ask. But there's more to the decisions than everything that comes out and fundamentally that board sat together and took what their best [decision] was from what they had on the table, for all the reasons that come into it."

Kubica was eventually named as the Williams reserve and development driver for this season, leaving di Resta without a position after two years in that role for the team.