Carlos Sainz could be let go by Renault if Red Bull does not quickly sign up its drivers for 2019.
That is warning of Cyril Abiteboul, the Renault team boss.
'We are not waiting forever'
Currently, Spaniard Sainz drives for Renault but he is 'on loan' for a year from Red Bull.
He is first in line to be called up by Red Bull should Daniel Ricciardo not renew his contract for 2019.
"We're not going to wait forever for Ricciardo and Red Bull to decide.
Either things can be put in place quickly with Carlos, and he would be an extremely serious option for next year, or we will consider alternative options," Abiteboul told L'Equipe.
It is believed Esteban Ocon, a Mercedes driver who currently races for Force India, is one of those options.