Paddy Lowe says that if Williams makes a driver change within 2019, it will be Robert Kubica who steps up to the plate.
It is strongly rumoured that either by Singapore or Russia, Lance Stroll will leave Williams to join his father at the newly Lawrence Stroll-owned Force India.
When asked by Nextgen-Auto about the Stroll story, Williams boss Lowe said at Monza: "We don’t really have to do anything because Robert Kubica is our reserve driver.
"All we can do is wait for events to unfold, but it’s not a certainty that anything will unfold. At the moment we are focusing on working with Sergey and Lance," he said.
Lowe also played down rumours that Williams is going to start using the full Mercedes gearbox from 2019.
"We produce our own gearbox and we’ll continue to do so," he insisted.
Williams is now the only team in the pitlane that uses an aluminium gearbox, and Lowe would not comment on whether it will switch to titanium for 2019.
As for why he rejected the Mercedes gearbox option, he answered: "We discussed it but decided it wasn’t an option for Williams."