Claire Williams has reiterated that the team's only focus at the moment is the current season and would not be drawn on Felipe Massa's future.
The Brazilian was due to retire at the end of the 2016 season but was drafted back in by Williams after Valtteri Bottas made the move to Mercedes.
Massa feels he is still competitive enough to extend his stay by another year, but has admitted he will more than likely join Formula E once his Formula 1 career is over.
Claire Williams has consistently stated that the team are in no rush to confirm their 2018 line-up as it is not a priority at this stage.
But, the longer the delay, the more doubtful it seems that Massa will be retained.
"Felipe has done a fantastic job, it’s been a bonus year for us. He very kindly came back and he’s really delivered for us," said Williams.
"Obviously the past couple of races have been tough for him with his medical issue [in Hungary] but we’re through that now and we’re looking forward to him delivering for the rest of the year and we really just have to wait and see."
Robert Kubica and Sergio Perez have both been linked with Williams in recent weeks.