Alexander Albon looks to have definitely secured the second Toro Rosso seat for 2019.
Daniil Kvyat is already signed up, and team boss Franz Tost admits that Brendon Hartley has not done enough this year to guarantee the other place.
"He has 4 points, Pierre (Gasly) has 28. That means he has to improve his performance if he wants to stay in the team," he said.
Germany's Auto Motor und Sport said Albon, a Briton with Thai heritage, has secured the backing of Red Bull owner Dietrich Mateschitz's Thai partners.
Red Bull has already negotiated the end to the 22-year-old's Nissan contract in Formula E.
However, the energy drink company doesn't want to announce the deal until after the season finale in Abu Dhabi.
"You will hear from us in Abu Dhabi," confirmed Dr Helmut Marko.
For New Zealander Hartley, it will be an uncomfortable wait.
"I have a contract for 2019. They just have to tell me if they want me or not," he said.
"I did my best ever formula one race in Austin. I think if you just look at results, it doesn't show what I've done for the team. I could have many more points."
