Red Bull are clinging to their "reserve driver" Carlos Sainz, according to the energy drink marque's Dr Helmut Marko.
Some are raising their eyebrows after Renault, who earlier made a bid to sign Spaniard Sainz for 2017, unveiled a new F1 sponsorship deal with Spanish company Mapfre.
"Historical affinities between Renault, F1 and Spain are once more alive thanks to this partnership," said team boss Cyril Abiteboul.
Sainz, 22, impressed particularly in 2016, but despite Renault's interest Red Bull are insisting upon their contract with the Spaniard and keeping him at the junior team Toro Rosso.
Spanish daily AS quotes Red Bull driver manager Marko as saying: "We have a long term contract with Carlos and the situation at Mercedes shows how important it is to have reserve drivers.
"Sainz is clearly our reserve driver in case anything happens at Red Bull Racing."
After a season with year-old Ferrari engines, Toro Rosso are moving to up-to-date Renault power for 2017, and technically closer to Red Bull in other areas as well.
Marko explained: "Toro Rosso has to achieve better results so we have the target of fifth place for them in 2017.
"With a good designer like James Key they have the potential, and we see it as positive that both drivers (Sainz and Daniil Kvyat) are staying because that provides stability.
"They are a good mid-table team and what Carlos was offered [by Renault] was no better than that, or worse."
The 2017 season gets underway in Melbourne next month.
