Valtteri Bottas' switch to Mercedes from Williams appears imminent after the latter's deputy team principal, Claire Williams, revealed a deal was close to being finalised.
Bottas swiftly emerged as the favourite to fill the vacancy at Mercedes left by the shock retirement of Formula One world champion Nico Rosberg on December 2.
Asked at the Autosport International Show if it was now a case of crossing the t's and dotting the i's on a move, Williams said: "It's exactly that.
"I suppose as soon as Nico made the announcement, I knew the call was going to come from Toto [Wolff, the head of Mercedes-Benz Motorsport]. I know that he's admired Valtteri and I think many people do admire Valtteri's talent.
"You don't want to stand in the way of a driver that has an opportunity to go and race in a car that's winning races, winning world championships.
"Everybody knows Ferrari were after Valtteri in 2015 and we stood in his way, and he stood by us. And I think you have to do the right thing sometimes.
"But we also, as a team, have to do the right thing by the 650 other employees that we have at Williams. So we need to make sure that if we are to release Valtteri, then we have the best credible option to replace him."
Felipe Massa, another driver to have retired at the end of last season, has been strongly linked with a return to Williams, who will have Canadian rookie Lance Stroll in one of their cars in 2017.
"I wish I could announce who it was, we are still crossing the t's and dotting the i's at the moment with all of the contracts," Claire Williams added.
"We will be making an announcement shortly because we are testing soon and we all want to know who's going to be driving for us."
Williams also insisted her team were not being forced to release Bottas due to their status as a client of Mercedes.
"People mistake this quite regularly, that just because we're a customer of Mercedes, Toto picks up the phone to me and I go 'alright, then'," she explained.
"It has to be to the benefit of Williams if we're ever going to agree to anything. We are a customer of Mercedes; we aren't a junior team; we aren't a B team to them or a sister team. We pay for our engines, we pay on time and therefore they don't have any rights to come to us and say 'you need to release this driver for us now'.
"It has to be in our best interests and we are entitled to make the decision that we want to. And there is no negative outcome if we don't. If we decided not to release Valtteri, then Mercedes would be fine."