Red Bull consultant Helmut Marko has revealed that Daniil Kvyat is not under consideration for a 2020 seat at the senior team.
Kvyat will stay at Toro Rosso for another season but Red Bull is yet to decide on whether Pierre Gasly or Alexander Albon will partner Max Verstappen.
Verstappen, who stepped up to Red Bull mid-2016, is already on a 2020 contract, but the team has been fluid with its second seat.
Gasly stepped up for 2019 in place of Renault-bound Daniel Ricciardo but struggled for performance through the first half of the campaign.
Gasly had been assured that his seat was safe through the rest of the year but a few days into the summer break senior Red Bull figures changed their stance.
Albon, who stepped up to Formula 1 with Toro Rosso for 2019, was promoted to Red Bull after just 12 grands prix, with Gasly returning to the junior outfit.
“We will make our evaluation after Mexico,” Marko explained to Sky Sports in Singapore.
“It’s already Kvyat confirmed [at Toro Rosso] for next year, or at least internally its clear. Then it’s between Gasly or Albon [for Red Bull].”
The Red Bull seat is the only current vacancy at a front-running team, with both Mercedes and Ferrari having confirmed their unchanged 2020 line-ups.
Elsewhere just Alfa Romeo and Williams have an available seat.