Toro Rosso team boss Franz Tost says he does not expect its 2019 Formula 1 driver line-up to be finalised until December.
Toro Rosso has fielded Pierre Gasly and Brendon Hartley this year but the Frenchman will move up to Red Bull next season as a replacement for Renault-bound Daniel Ricciardo.
Toro Rosso has already revealed that Daniil Kvyat will return for a third stint but it has yet to confirm the identity of his team-mate.
Hartley has stressed that he holds a 2019 contract but Red Bull has been in negotiations with Formula 2 front-runner Alexander Albon.
Albon signed a three-year deal to race for Nissan in Formula E but did not participate in pre-season testing last week.
Hartley scored a career-best ninth last weekend in the United States, following the exclusion of Esteban Ocon and Kevin Magnussen, but Tost emphasised the New Zealander still needs to improve.
“He showed a good race in Austin, but nevertheless if you look to the results he has four points, Pierre has 28 points,” said Tost on Friday.
“That means he has to improve his performance if he wants to stay in the team.”
On a deadline for a decision, Tost commented: “First of all we have to finish the season to get a clearer picture.
“Then I assume in December Red Bull will decide the driver line-up of Toro Rosso.”
Tost added that Albon is “of course” on the list, but added “you know negotiations are confidential, [so] I can’t give any details about it.”
Toro Rosso is one of only three teams yet to confirm its full 2019 driver line-up, though of those trio Force India is poised to field Lance Stroll alongside Sergio Perez.
