It appears likely the French team will oust Jolyon Palmer, and the highest profile candidate to replace him would be former Renault champion Fernando Alonso.
However, boss Cyril Abiteboul and Alonso himself have played down claims of a Renault reunion, and now team advisor Alain Prost agrees a deal is unlikely.
“We cannot offer Fernando a winning (car) next year, which is very difficult for a driver of this calibre,” he is quoted at Monza by the Times newspaper.
But Prost doubts Alonso will quit F1 if he cannot find a winning car somewhere in pitlane.
“For us it would be very good to have him, as we want to win and he would be a very strong piece of that,” he told the Spanish broadcaster Movistar.
“Fernando knows that we cannot offer him a champion car in 2018 but in any case I don’t see him leaving formula one at the end of the season,” said Prost.
The other high-profile candidate to join Nico Hulkenberg in 2018 is Robert Kubica.
“He has done well,” Prost said. “The test at Valencia was particularly surprising.”
But also in the running are Carlos Sainz, Sergio Perez and perhaps even Red Bull junior Pierre Gasly, who is French.
“We have a few drivers that we are considering for the future. We want to set ourselves up before Singapore,” added Prost.