Red Bull have defended their decision to part ways with Daniil Kvyat, saying the time was right to look to the future.
As reported by Sky Sports on Wednesday, Kvyat has lost his Toro Rosso seat and been dropped from the Red Bull stable to end a relationship which began in 2010, when the Russian was 15 years old.
Red Bull have been criticised in some quarters for the decision, with Kvyat brought back after a two-race absence last weekend in Austin only to be shown the door despite finishing in the points on his return.
However, after four seasons and 72 races in the sport in which he has driven for both of the energy drink company's teams, Christian Horner believes the time is right for Kvyat and the Red Bull family to move on.
"Dany Kvyat has obviously had a large investment from Red Bull over the years," said the Red Bull team boss at the Mexican GP.
"He had the opportunity to step into Red Bull Racing and compete in the 2015 season and the start of the 2016 season with the team. Formula 1 is a tough business and unfortunately Dany didn't do enough, in our opinion, to warrant retaining that seat.
"But we still believed in him and he was given a second opportunity, which is very unusual in Formula 1, to retake the seat with Toro Rosso.
"And then from there we obviously have other juniors that we have invested in that are knocking on the door of Formula 1."
The drivers in question are 21-year-old Pierre Gasly and 27-year-old Brendon Hartley, who are racing for Toro Rosso in Mexico this weekend and are now set to see out the season.
Horner described them as "two exciting prospects for Red Bull Racing potentially further down the line" and Franz Tost, Toro Rosso's team principal, has dropped a strong hint that they will form the team's 2018 line-up.
"Both are Red Bull drivers, both are high-skilled drivers, fast drivers and we want to test them for the rest of the season, because there is a high possibility that this will be the driver line-up for 2018," said Tost.
Kvyat's F1 options for 2018 now appear thin. Horner told Sky F1 that the Russian would represent a good fit for Williams, but the 23-year-old would appear to be behind Robert Kubica, Paul Di Resta, Pascal Wehrlein and Felipe Massa for the one vacant seat at the Grove team.