Felipe Massa says that he does not have any realistic options other than Williams if he is to remain in Formula 1 in 2018.
Massa signed a one-year deal to stay in the championship this year after Valtteri Bottas shifted to Mercedes to replace Nico Rosberg.
His future beyond that is up in the air, and Massa has previously said that he does not want to be treated as a last resort by Williams again.
When asked if it was Williams or nothing next year, Massa said, “I think so.
“Or maybe something happens, a guy like Rosberg decides to retire.
“But I don't think it will happen.”
Massa said he had enquired elsewhere about a seat but could not find a suitable project and was no longer talking to any team but Williams.
“I looked but maybe teams that I looked at had a different direction in terms of drivers,” he said.
He has previously said he will head to Formula E if he leaves F1, but 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,” said Massa.
“I need to be sure maybe I can have a better year.”
According to a report in Autosport, Williams has a three-driver shortlist to partner Stroll.
The candidates are Massa, Robert Kubica and current reserve driver Paul di Resta, who impressed when standing in for an unwell Massa in Hungary.
Sources suggest Williams is in no rush to make a final decision as it is in a strong position given the lack of vacancies elsewhere.
It is also planning to give Kubica some mileage in a 2014-spec car in a private test.