Toro Rosso has ruled Dan Ticktum out of the running for the second Toro Rosso seat alongside Daniil Kvyat for 2019.
Ticktum, a 19-year-old Briton, is a title contender in European F3, but at Sochi he was chided by Red Bull boss Christian Horner for recent comments made about Mick Schumacher.
'He is a gifted driver'
Horner also said Ticktum is not ready for Formula 1, and Toro Rosso boss Franz Tost agrees.
"He is a gifted driver, but it seems to me that it is too early for him to go to F1.
"He needs another year or two in Super Formula or Formula 2. F1 is now very complex and very fast and to go straight from Formula 3 with the current F1 regulations is very difficult," Tost said.
Ticktum also doesn't have an F1 super license, which earlier frustrated Red Bull driver boss Dr Helmut Marko.
Toro Rosso seat speculation
But Tost said: "I like the super license rules. It means the drivers who come to F1 have the necessary skills and experience."
Media reports say Pascal Wehrlein or Mick Schumacher are in the running to be Kvyat's 2019 Toro Rosso teammate.
But Marko says Brendon Hartley could keep his seat after all.
"He has the rest of the season to prove himself. He has to beat Pierre Gasly and he knows that too. But leaving him in the car would not be the worst solution," he said.
Marko insisted that Esteban Ocon would only be a contender if he was "free from all contracts", but both the Frenchman and Toto Wolff have said he will remain a Mercedes-backed driver.