Sep.3 - Renault looks set to complete its 2018 driver lineup prior to Singapore in a fortnight.
"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.
"He has done well," Prost said. "The test at Valencia was particularly surprising."
"We have a few drivers that we are considering for the future. We want to set ourselves up before Singapore," added Prost.
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