Felipe Massa has suggested it is Williams or nothing if he is to stay on in Formula 1 for the 2018 season.
Williams convinced Massa to come out of retirement to partner Lance Stroll this season, after Valtteri Bottas moved to Mercedes to replace world champion Nico Rosberg.
The Brazilian agreed a one-year deal and though he is in talks with Williams over a fifth season with the outfit, a firm decision has yet to be made.
Massa has said he needs Williams to show it wants to keep him and that he does not want to be seen as a last resort when no other suitable drivers are available.
When asked if it was Williams or nothing next year, he said: "I think so. Or maybe something happens, a guy like [Nico] Rosberg decides to retire. But I don't think it will happen."
Massa said he had enquired elsewhere for a seat but could not find a suitable project.
"I look but maybe teams that I looked, maybe they had a different direction in terms of drivers," he said. "Now no [talks with other teams]. Now I check if I stay or not. "
Massa, who has previously said he will head to Formula E if he leaves F1, added he has yet to decide what he wants to do.
"I'm still thinking, I'm still talking with the team, to see if they want me or not. I need to be sure maybe I can have a better year."
Motorsport.com understands Williams has slimmed its shortlist for the seat alongside Stroll down to Massa, Robert Kubica and current reserve driver Paul di Resta, who delivered a strong performance when standing in for Massa in Hungary.
Sources suggest Williams is in no rush to make a final decision given it is in a strong position amid a lack of vacancies elsewhere.
It is also planning to give Kubica some mileage in a 2014-spec Williams in a private test.