Renault e.dams Formula E boss Alain Prost says he would have released Sebastien Buemi to contest Formula 1's US Grand Prix with Toro Rosso, but Red Bull never asked.
Prost, who also acts as a special advisor for the Renault F1 team, confirmed he would not have let Buemi out of his Formula E contract to race full time for Toro Rosso in 2018, which may have scuppered the Swiss driver's chances of running in Austin.
Ultimately, Toro Rosso chose to take Brendon Hartley, a driver who would be available to race in 2018.
"Sebastien called me and [I] said I have no problem if you have an offer to make the race here," Prost told Autosport.
"But not for next year, because we have a contract, and we cannot release a driver one month before the season. Formula E is a strong programme, with a constructor.
"But we have never been asked officially. Sebastien just called me and said, 'If I have an offer, can I do the race in Austin?' and I said, 'yes, but be careful because not for next year.' But he didn't have any offer."
Prost is convinced that Buemi would do well if he ever does return to F1.
"I think he had the potential for staying in F1, and the way he stopped his career was very bad, but what can I do?" Prost added.
"We never had this discussion in the last three years - that we were together for him going back to F1, never.
"I'm sure he would do a good job, but Formula E is also going up, and we need a driver like that.
"If we'd had this discussion six or eight months ago, it could have been different."