By Alan Baldwin
MEXICO CITY (Reuters) - New Zealander Brendon Hartley and French rookie Pierre Gasly are likely to be retained as Red Bull-owned Toro Rosso's Formula One lineup next season, team principal Franz Tost said on Friday.
"We want to test them for the rest of the season because there is a high possibility that this will be the driver lineup for 2018," the Austrian told reporters at the Mexican Grand Prix.
Dropped Russian Daniil Kvyat has meanwhile left the Red Bull driver program and is now a free agent.
Hartley was drafted in for the U.S. Grand Prix in Austin and is paired with Gasly, who missed the race in Texas, for the first time this weekend.
Kvyat, 23, was dropped by the Red Bull-owned team for the second time this season after last weekend's race. He had already been demoted by Red Bull in 2016.
"(Kvyat) is not any more with Red Bull and therefore he is free to decide whatever he wants to do," said Tost.
The principal said he was really happy that Le Mans 24 Hours winner Hartley, who tested for the team in 2009 and was then dropped, had returned and indicated clearly that he saw him in the car beyond this season.
"Brendon is a very high skilled driver, very committed, passionate for motorsport... if we give him a competitive car, he will be there and he will also fight in Formula One for success.
"And I hope that especially next year we will bring together a competitive package that he can also fight for victories and good positions," added Tost, whose team are switching to Honda engines.
The Honda power unit has been woefully uncompetitive with McLaren this season.
Red Bull team boss Christian Horner said Hartley's was a fantastic tale of redemption and determination.
"That is a guy who started off life on the junior program, he got dropped early on in his career -- there was no remorse, no 'poor me' or 'haven't I been badly treated'. He thanked Red Bull for the opportunity and endeavored to stay in touch.
"He had nothing else to race. He went back to racing Minis, to racing historic Formula One cars. Anything he could get his hands on, he raced. And he showed a passion and a commitment to keep doing what he believed in and himself as a race car driver."
Hartley, now 27, then renewed the relationship with Red Bull when he joined the Porsche sportscar program and won the world endurance championship.
"I think it testimony to him, his determination and tenacity and skill and talent that he's got himself back into a position that he's been selected to be in the Toro Rosso car," said Horner.
Kvyat, he said, had been given plenty of chances but ultimately "didn't do enough to warrant retaining the seat."
(Reporting by Alan Baldwin, editing by Ken Ferris)