Cape Town - Robert Kubica believes he is "ready" to step up to a Williams race seat at any time should Lance Stroll leave the team.
With his father Lawrence now the new owner of the Racing Point Force India team, there has been some suggestion that Stroll could swap teams during this year's championship.
Asked about the rumours in the build-up to the Belgian GP, the driver replied "nothing's guaranteed."
He added: "For the moment, I am here at Williams. I am not sure what I will be doing in the future."
Should Stroll swap to Force India, Williams could call on reserve driver Kubica to replace him.
The Polish driver has spent time in the car testing for the team and believes he is ready to race if they need him.
"I feel ready because otherwise I would not sign a contract with Williams for this year," he told Autosport.
"So it's on my desk that, 'You have to keep being ready and in case something happens, you have to step up'.
"Of course, it is not easy when you have to drive against the top drivers in the middle of the season.
"Although I have some opportunities to drive the car, you still lack experience, but you have to do it.
"I also think when Williams approached me for this role, they also have no doubts that I can do it.
"But what's happening currently and a lot of speculation is not affecting myself.
"I'm doing my job and then what the future will bring, we will see."