Toro Rosso have replaced Daniil Kvyat with Red Bull reserve driver Pierre Gasly ahead of the Malaysian Grand Prix as they look to firm up plans for 2018.
GP2 champion Gasly will make his Formula One debut at Sepang this weekend, having tested extensively for Toro Rosso's sister team in the past - including at Hungary this year.
Toro Rosso had been widely expected to give the 21-year-old Frenchman a run in the remainder of the season, with Carlos Sainz Jr set to join Renault in 2018 as part of the convoluted engine deal which will see the Red Bull feeder team supplied by Honda, whose relationship with McLaren has been terminated.
It had been reported that Sainz could join Renault as early as this term, but Jolyon Palmer's career-best sixth-place finish in Singapore appears to have saved the Englishman until the close-season, when he faces a battle for an F1 seat - Williams his most likely destination.
A Toro Rosso statement did not outright confirm which races Gasly will take part in, although he is highly unlikely to compete at the United States Grand Prix as it clashes with the final round of the Japanese Super Formula Championship. Gasly is second in the standings of that competition.
Gasly said: "This is a great opportunity for me. I feel as ready as I can be, having had to be prepared for anything in my role as Red Bull Racing's third driver this year.
"I will do my best to perform well with Scuderia Toro Rosso during these coming races."
Toro Rosso insist that Kvyat "still remains part of the Red Bull family", but his dropping from a Red Bull-owned team for the second season in a row will raise eyebrows.
He made way at the Austrian team for Max Verstappen after a collision-filled start to 2016, while the Russian has only scored points in two races this term - his haul of four vastly outweighed by the 48 that Sainz has accrued.