Pierre Gasly, who raced at Sepang and Suzuka for Toro Rosso, will contest the final of the Super Formula series in Japan rather than the US GP in Austin next week.
Gasly was promoted to a race seat with the Faenza-based and replaced Dany Kvyat in Malaysia and Japan. The Russian will return to Toro Rosso for Austin but with Carlos Sainz moving over to Renault earlier than expected and Gasly absent, it is unknown at this time who will be sitting on the other side of Kvyat's garage at the Circuit of the Americas event.
It was initially believed that Honda preferred to see the French driver defend his chances of clinching the Super Formula crown, but the manufacturer later considered the US GP to be its priority.
Toro Rosso boss Franz Tost is now apparently keen on evaluating another driver in Austin, thus forcing Gasly's return to Super Formula.
It is expected however that the 21-year-old will resume his F1 stint for the remaining races in Mexico, Brazil and Abu Dhabi.
Both Robert Kubica and Indy 500 winner Alex Rossi, initially believed to be in with a chance of racing for Toro Rosso in Austin, have been ruled out.
Penske's Josef Newgarden is also an unlikely contender despite Liberty Media suggesting the presence of an American driver on the grid in Austin.
With a lack of young talent behind Gasly, it's anybody's guess who Toro Rosso will enter next week. Former team member and Red Bull-sponsored driver Sebastien Buemi could be a possible choice but his WEC Toyota connection would likely make his return a complicated affair.