Dr Helmut Marko says Alexander Albon needs to "earn his seat" in 2020.
"He has to earn his seat," Marko said, when asked what the British born Thai driver needs to do in 2020.
But Marko says more Red Bull junior drivers are now waiting for a chance to push into F1.
"During the first negotiations about these races in Spielberg, we campaigned for Formula 2 and Formula 3 to be there too," said the Austrian.
"That is more important for us than for the others, as we rely on these youngsters. We need to see how they are going.
"We have two drivers in Formula 2 and three drivers in Formula 3. Our driver choice for 2021 is based on who is quick and worthy enough to step up," Marko added.
Marko thinks the entire driver market could be shaken up if driver salaries are added to the team budget caps in future.
"Petronas only has to transfer a little less to the team and send it to Hamilton instead. A limit on the driver salary is essential," Marko insisted.
"Of course we still have to fulfil the current contracts, but we must do something in this area as soon as possible."