The Grove-based squad is evaluating whether Sargeant is making the necessary progress in his rookie season to justify being given another year in the car.
Although the American has shown some promising speed for the team, he has yet to score a point and has had a spate of accidents along the way.
Team boss James Vowles made it clear after another crash in Japan that he still had faith that Sargeant could step up enough, and that the scenario he was eyeing was them continuing together next year.
Asked at the Qatar GP about the time frame for making a call, Vowles insisted there was no rush and he was willing to give Sargeant every opportunity to show what he could do.
"I suspect it'll be to the end of the season," said Vowles. "I think we've already committed to the direction of travel we're in.
"He has targets to hit and it'd be wrong to go against that decision point. So end of the year."
Vowles explained that Williams was so willing to be patient with Sargeant because it saw the potential that the youngster was delivering – and all that it needed to see was him putting together more complete weekends.
"The pace is there," added Vowles. "That's the thing that we wouldn't be able to fix or repair.
"But what happens is, when it comes down to the crunch time, there are elements of inconsistency that creep in, and in form of that, goes into an accident sometimes.
"In Suzuka the lap he did was, line-on-line on the data with Alex [Albon], but obviously it's marred by the fact that the last corner, he had far too aggressive a throttle application and there was a crash, and a significant crash as a result of it.
"What we're working with him on is actually the progression up until that point. He dialled it from two seconds away from Alex to within a tenth in FP3 – in fact, he was faster in FP3. And it's actually keeping that mindset all the way through that we're trying to do."
He added: "We have – and I've said this publicly – a responsibility to invest in our rookie drivers. We've put him there, and we've given him nearly no testing mileage.
"I'm used to 30,000km, not 850km. But what we want to see is continued progress and now a focus on making sure we keep that consistency in there, which will then deliver results."
Too good a start
Vowles believes that one factor that may have worked against Sargeant was almost too good a start to his F1 career in the Bahrain Grand Prix.
In qualifying, he matched Lando Norris' time in Q1, although failed to make it through to Q2 because his McLaren rival had set his laptime before.
Vowles thinks that that moment may have left Sargeant feeling he was well on top of things, so when the season hit a tougher patch it was harder to deal with.
"Probably the worst thing that can happen [was] he went into Bahrain and overlapped with Lando in terms of Q1," said Vowles.
"He thought perhaps the challenge in front of him may not be as significant as it really is.
"What you then saw after that time… and Alex has grown, I think across this season, and the gap started to grow, is you found a driver that's now frustrated.
"His normal tools aren't producing the quality of laptime that was there previously. He knows how to win.
"He's won in Formula 3, won in Formula 2 but applying that now in Formula 1 and then not achieving results creates more and more frustration – and then that ends up with over-driving, fundamentally. That's the dialling back bit."
