MEXICO CITY (Reuters) - New Zealander Brendon Hartley must do better if he wants to stay with Toro Rosso next season, team boss Franz Tost said on Friday with a final decision on the lineup likely to be made in December.
Hartley has fared badly compared to French team mate Pierre Gasly so far this season and his future in Formula One remains uncertain.
"He showed a good race in Austin. But nevertheless, if you look to the results, he has four points, Pierre has 28 points," Tost told reporters at the Mexican Grand Prix.
"That means he has to improve his performance if he wants to stay in the team.
"First of all, we have to finish the season to get a clear picture and then I assume in December Red Bull will decide the driver line-up of Toro Rosso," he added when asked about a deadline.
Gasly is moving up to the main Red Bull team next year alongside Max Verstappen, with Russian Daniil Kvyat returning to Toro Rosso as his replacement.
Toro Rosso is the feeder team for Red Bull, giving debuts to rookies from within their young driver programme, but the conveyor belt of talent is facing a shortage of supply.
That could help Hartley's prospects, although Toro Rosso are interested in Thai-British driver Alexander Albon who is second in the Formula Two standings.
Albon recently agreed a deal to race in the all-electric Formula E series with Nissan, but did not take part in recent pre-season testing in Spain.
Tost confirmed the 22-year-old was in the frame but said negotiations with Nissan for the driver's release were confidential.
The Austrian also praised engine partners Honda, who will also be supplying Red Bull next year, for exceeding expectations about reliability.
"We thought we would have much more problems but to be honest we haven’t had any major issues, and also regarding the performance, because with the new specification we are not far away from the top teams," he said.
(Writing by Alan Baldwin in London, editing by Pritha Sarkar)