Red Bull team principal Christian Horner says Carlos Sainz will remain a driver for sister team Toro Rosso next year.

Sainz said earlier this week it was "unlikely" he will be driving for his current team next season, but Horner has stressed the 22-year-old is under contract for the 2018 campaign.

"He’s under contract. We’ve exercised his option as well, so he’s under contract," he told Sky Sports. "We have an option on him for next year and the year after, so he’ll be in a Toro Rosso again next year."

Sainz has impressed in the eight races so far this season, with points in six GPs to leave him 25 ahead of team-mate Daniil Kvyat.

The Spaniard has been linked with a move away from Toro Rosso as a result of his performances but a promotion to Red Bull appears unlikely, with Daniel Ricciardo and Max Verstappen in possession of those seats.

Sainz said he would look elsewhere if a Red Bull ride was not an option for 2018 but Horner has ruled out a Toro Rosso exit for the youngster.

"Well I don’t know where he thinks he’ll be then. Contracts are clear," Horner added when Sainz's comments were put to him.

"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."