Paul di Resta is out of the running for a seat with Williams in 2018 despite "a very good test" with the Formula One team.
Williams are the only team in the paddock yet to announce their line-up for the new season following Felipe Massa's retirement, which left a space alongside Lance Stroll.
A host of names have been linked to the vacancy, including Robert Kubica, Pascal Wehrlein, Daniil Kvyat and Sergey Sirotkin.
Di Resta was also in the mix for a permanent drive with the British team after impressing during his sole outing in 2017, when he replaced an ill Massa in Hungary.
He will not be with the team going forward, though, after revealing Williams have informed him of their plans to look elsewhere.
"I don't think it's any secret I'm not going to be doing it," he told Express Sport. "I'm not in the plans at the moment. What else they do, I don't know. They've got a few other guys in the equation.
"Sirotkin, Daniil Kvyat is out of it, Pascal was maybe cruising around. I don't know which direction they're going to go.
"Absolutely [I wanted that seat] and I was only told very, very late December that I wasn't in contention any more. I had a couple of good years there, I would obviously have wanted to do that more.
"I had a very good test when they did the 'driver assessment' if you want to call it [that]. I was very happy with how that came out.
"But for whatever reason, there are various other things that go [into getting] that seat."
Kvyat – who was demoted by Red Bull to Toro Rosso in 2016 before being dropped altogether after earning just five points last season – is out of the running after being signed by Ferrari as their development driver.