Robert Kubica says his future will become clearer "sooner or later".

The popular Pole returned to F1 this year after an eight-year break following his near-fatal rallying crash of 2011.

But he has struggled, not just with Williams' slowest-in-2019 car, but notably against his teammate George Russell.

"Unfortunately this season is much harder than it looks, not only from a driving point of view," Kubica told tuttmotoriweb.com.

"Being back after eight years was difficult, but in a regular season I think I would have the chance to do well."

Team boss Claire Williams already has Russell under contract for 2020, and does not hide that there is uncertainty about the other seat.

"We're working out what we're going to be doing from a race driver perspective for 2020 at the moment," she said at Monza.

The 2020 'silly season' is now in full swing, but whether Kubica can stay in Formula 1 is not at all clear.

"I have an idea of what is possible and what is not, and what I would like to do," the 34-year-old told reporters at Monza.

"Sooner or later, a decision will be made, then it will become clear what I will do next year."

Asked if he has done enough to keep his Williams seat, Kubica added: "I don't know.

"As I said, first I need to take a decision for myself, and then we will see what is possible."