Vandoorne will leave McLaren at the end of the 2018 season. The 26-year-old has had a tough year, last scoring points at the Azerbaijan Grand Prix. He is also yet to out-qualify teammate Fernando Alonso this season, leading McLaren to take the decision to drop him.
He will be replaced by Lando Norris, McLaren's current reserve driver. Toro Rosso, Red Bull's junior squad, has already filled one of its seats for 2019 with Daniil Kvyat, however it is not known who will partner the Russian next season.
But Marko assures that it won't be Vandoorne: "We will not take Stoffel," Dr Helmut Marko told the broadcaster RTBF. "I think he's just not fast enough for F1."
It seems almost set in stone that Vandoorne will instead leave F1 altogether and join the new works Mercedes team in Formula E: "I have always liked Stoffel, a brilliant driver in the junior categories," said Mercedes boss Toto Wolff.
"We must now try to understand why it did not work for him in F1, but maybe there could be some news about him soon. I think his character and speed would work very well at Mercedes, but for now we will have to see," the Austrian added.
Bahrain International Circuit - Winter testing