Esteban Gutierrez has emerged as a shock candidate to take Williams' second seat alongside George Russell in 2019. The Mexican driver has claimed he has "chances" to return to Formula 1, with the only other vacant seats at Force India and Toro Rosso expected to go to different drivers.
Lance Stroll is a near certainty to take Force India's remaining seat after his father's takeover of the team, while Toro Rosso are thought to be evaluating between retaining Brendon Hartley or signing Alex Albon to partner Daniil Kvyat.
Williams have already signed Mercedes junior Russell and have also been linked with Robert Kubica, Esteban Ocon and Nyck de Vries.
Williams will lose title sponsor Martini in 2019 and saw a potential deal with Rich Energy fall through when the drink company signed a deal with Haas, so the well-backed Gutierrez could be of interest, having kept his hand in F1 since leaving Haas at the end of 2016 by working as a simulator driver for Mercedes.
"I am working very hard, I've been preparing a lot this year, I am very motivated," said Gutierrez.
"I've been working with Mercedes, a very professional team, actively on the simulator, doing different things, and I am really positive about the future.
"I think I feel like I have a lot to give in Formula 1, and I am very motivated for it.
"I have chances, I am here. At the beginning of the year I was not involved with a Formula 1 team and now I am with Mercedes, which is at the moment one of the most important teams in Formula 1.
"I've been working very hard, it hasn't been easy, but I am really positive about the future. I think there is a lot to come in my career, and there is a lot I can give as well."
On Williams, Gutierrez added: "It is a great team. It is one of the most respected teams in Formula 1.
"I think they've had difficult years, but the people they have and the team they are I am pretty sure they can recover pretty well."
Gutierrez raced for Sauber in 2013 and 2014, and spent 2015 as a test driver for Ferrari before teaming with Romain Grosjean in Haas' debut campaign in F1, although he failed to score a single point and was replaced by Kevin Magnussen.
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