Both drivers are out of contract at the end of this year and the growing feeling is the duo will trade places for next season.
That will see Bottas returning to Williams, the team where he started his F1 career, with Russell finally getting his promotion after three years with the back-of-the-grid outfit and forming an all-British driver line-up at Mercedes with Lewis Hamilton.
Marko's words are unlikely to be welcomed by Mercedes whose team principal Toto Wolff recently traded verbal blows with Red Bull counterpart Christian Horner over the recent flexi-wing furore.
Speaking to F1 Insider with regard to the Russell-Bottas trade, Marko said: “You can't hold it off any longer otherwise the funding no longer makes sense, even if Hamilton won't be happy."
As for Bottas, Marko added: "Bottas doesn't have to call us. There is no space. Actually, I can only imagine a swap with Russell. I think Williams will be the only option for him."
Russell decision out of Williams' hands
Marko's comments indicate Red Bull will opt to retain Sergio Perez alongside Max Verstappen for next season when it appears the driver market will remain stable.
Hamilton has indicated his desire to continue with Mercedes, beyond which the seats at McLaren, Ferrari and Aston Martin are filled for 2022.
Although Esteban Ocon is out of contract with Alpine he appears certain to remain, leaving very limited options available for Bottas, underlining Marko's comments that Williams is his best bet.
New Williams team boss Jost Capito recently told Sky Deutschland: “We would like to keep George, but we all know that Mercedes will make the decision."
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