Daniil Kvyat’s return to formula one with Toro Rosso next year will be announced on Saturday.
Earlier, it was reported that the Russian’s 2019 contract will be unveiled on Friday.
But sources at Sochi say it will now happen on qualifying day ahead of the Russian grand prix.
Asked if it will be good news for Russian fans, Toro Rosso boss Franz Tost smiled: "It will be good news for all formula one fans."
The identity of Kvyat’s teammate is less clear.
Dr Helmut Marko hinted earlier that Red Bull could wait to see if Dan Ticktum gets a super license, but the F3 star has angered Christian Horner with negative comments about Mick Schumacher.
"He’s talented but he still has to develop before he is even close to F1," Red Bull boss Horner is quoted by Finland’s MTV.
As for Schumacher himself, Marko ruled that out, saying those stories are "completely out of thin air".
The other remaining unconfirmed places on the grid for 2019 are at Force India and Williams.
But Lance Stroll is definitely on the way to Force India, and Sergio Perez said in Russia that an announcement on his plans are due soon.
"I know what I’ll do and I think we will try to make an announcement in Mexico," he said.
As for Williams, Mercedes-backed Esteban Ocon visited the factory last week, but Toto Wolff says a "sabbatical" is also a big possibility for the Frenchman.
More likely is that struggling Williams needs to keep Sergey Sirotkin and his SMP Bank backing, and another well-funded Russian Artem Markelov is also in the running.
F2 driver Markelov is Renault’s reserve driver this weekend at Sochi.
"Yes, I thought I might have to replace Carlos Sainz," he said after running in practice, referring to the Spaniard’s eye and throat infection.
Asked how good his chances are of a 2019 race seat, Markelov told Ria Novosti news agency: "50-50. I will find out in a month and a half."