He will be replaced by George Russell, who joins from Williams, and is set to begin his assimilation into the team during the European autumn.
Meanwhile Bottas does not expect to engage much with his new employers prior to the season's conclusion in mid-December.
“I haven't been there yet,” he said of Sauber's factory.
“We've been in some contact but as I mentioned few weeks ago, the main focus is still fully on this season.
“We have a big job to do as a team and I need to keep my head in the right place.”
Mercedes currently leads the constructors' championship with a 36-point advantage over Red Bull.
With a maximum of 159 points still on the table for the drivers, Bottas remains mathematically in contention for the title.
He sits third in the championship behind Max Verstappen (262.5) and Lewis Hamilton (256.5) on 177 points.
Six races remain in 2021, including three in as many weeks as F1 takes in the United States, Mexico City, and Sao Paulo Grands Prix in quick succession from next weekend.
From there, a week off is followed by the inaugural Qatar Grand Prix, then a back-to-back for Saudi Arabia and Abu Dhabi.
After that, Bottas will join Alfa Romeo on a multi-year deal, at which point he'll familiarise himself with his new squad and its facilities as all-new regulations come into play for 2022.
“There will be the winter, the whole winter – whatever we get, two months – to prepare,” he said.
“I'm sure eventually I'll go there and start speaking a bit more, but still the main focus needs to be in this season.”
The United States Grand Prix takes place on October 22-24.