Pierre Gasly is set to fight for the Super Formula title at Suzuka rather than race for Toro Rosso in the Formula 1 United States Grand Prix, Autosport has learned.
Gasly, the 2016 GP2 champion, replaced Daniil Kvyat at Toro Rosso for Malaysia and Japan, and made it clear he would pick F1 over the Super Formula finale if he could.
Toro Rosso announced he would stay on for Austin, but Red Bull motorsport advisor Helmut Marko then suggested a final decision had yet to be made on where Gasly would race during the weekend of October 20-22.
Honda said it was its priority for Gasly to race at Austin, even if that meant it would sacrifice the Super Formula title to rival Toyota.
However, the Japanese manufacturer said it would welcome him back to Team Mugen if a replacement driver could be found for the US GP.
It has now emerged Toro Rosso boss Franz Tost is keen to run another driver in the second seat in Austin, alongside Kvyat, as he weighs up his 2018 driver line-up.
As a result Gasly, who trails Super Formula championship leader Hiroaki Ishiura by 0.5 points, will return to Team Mugen to contest the title.
Gasly is favourite to drive full-time for Toro Rosso next year and is expected to return to F1 to contest the final three races in Mexico, Brazil and Abu Dhabi.
It remains unclear who will replace Gasly at Toro Rosso in Austin with the team's options limited.