Sainz has a contract to race with Toro Rosso next year, but Renault has long been interested in trying to lure him away as it bids to ramp up its works efforts in F1.

With Renault's options for Stoffel Vandoorne, Sergio Perez and Valtteri Bottas having fallen away, it is understood that Sainz returned to the Enstone-based team's shortlist as a candidate for 2017.

But Red Bull sources have made it clear that there is no interest in doing a deal with Renault to let Sainz go - and his boss Tost has reiterated that he too sees no reason for the energy drinks company to want anything other than keeping him at Toro Rosso.

"Carlos has a contract with Red Bull, and I don't think Red Bull will let him go to another team considering the investment it has made during his career since the first steps in single-seater," Tost told Motorsport.com.

"Today he is a high-level professional, and I see no reason why he could be let go. Toro Rosso needs Carlos: he's fast, talented, and in 2017 we will need a driver of his level."

While Sainz has a contract with Red Bull, teammate Daniil Kvyat's future is still subject to speculation, with GP2 championship leader Pierre Gasly also a contender for the seat.

Tost admitted the second seat at Toro Rosso will be occupied by one of the two.

"There will be a noticeable change: wide tyres, new aerodynamics, and for a team like Toro Rosso it will be important to have at least one experienced driver. The ideal would be two," he said.

"It will be important to have an experienced driver like Sainz, then we'll see if Daniil Kvyat or Pierre Gasly will be alongside him. I see no other solution."

Interview by Roberto Chinchero