Red Bull Formula 1 chief Christian Horner is adamant that Carlos Sainz Jr. will be racing with Toro Rosso in 2018 despite the Spaniard's desire to move into a top seat.

Sainz has impressed throughout the early part of his F1 career, leading to speculation that he could be set to move up the grid from Toro Rosso for 2018.

Sainz said in Thursday's FIA press conference that a fourth year with Toro Rosso in 2018 was "unlikely", and that he would look elsewhere on the grid if a seat with Red Bull's senior F1 team was not available.

Speaking to Sky Sports, Horner said that Sainz remained under contract for next year, and that Red Bull intended to keep him at Red Bull.

"He's under contract. We've exercised his option as well, so he's under contract," Horner said.

"We have an option on him for next year and the year after, so he'll be in a Toro Rosso again next year."

When informed of Sainz's comments that he may not be racing for Toro Rosso next year, Horner said: "Well I don't know where he thinks he'll be then. Contracts are clear.

"You have to remember, he only got an opportunity in Formula 1 because of Red Bull investing in him in his junior years. It's a little disingenuous to be making comments like that.

"A lot of investment goes into these guys to give them an opportunity. Without Red Bull he wouldn't be sitting in a Formula 1 car."

Horner added that Red Bull would not consider loaning Sainz to engine partner Renault, believing Toro Rosso to be the best place for his development to continue.

"I can't imagine that scenario. Toro Rosso are ahead of Renault at this point in time and doing a good job so it wouldn't make sense to loan him out," Sainz said.

Horner was asked if Sainz had received a slap on the wrist for his comments, to which he replied: "He's just had one."