Carlos Sainz says he cannot spend his whole life waiting for Red Bull to promote him into the senior team.
The Spaniard agreed a new contract earlier this year which will see him remain at Toro Rosso in 2017, while Red Bull have both Daniel Ricciardo and Max Verstappen tied down to deals that run up until the end of 2018. Although Red Bull remains the target for Sainz, he admits he may have to look elsewhere to further his Formula One career if the senior team is not prepared to offer him a drive in two years.
"Unfortunately for me they look pretty happy with the pair they have," Sainz said. "Obviously it's good to have a third driver like me waiting there in case something happens, but I cannot spend my whole life being the just in case option for Red Bull.
"They understand this and I'm convinced they know -- that's why next year is an important year for me to hopefully create a good base and move up if Red Bull is willing to take me. Obviously it would be a great pleasure, if not I'm sure they will understand I cannot spend my life being the third one."
Red Bull has the option to extend Sainz' contract beyond next season, however Sainz expects he will have some say on his future and does not think Red Bull would try to stop him from leaving if another option became available to him.
"It depends obviously on them if they want to exercise that option but it will also depend on me if I also want to do another year in Toro Rosso," he said. "At the end they perfectly understand I have high targets, important targets in my mind for 2018 and it will be discussed.
"Red Bull is tough but they normally are fair. So I'm pretty sure Red Bull would, unless they said they really, really need me for a Red Bull seat, which I would be very happy with, I'm convinced they would be fair enough to find a solution."
The Spaniard added: "Like everything in life, like every contract in every Formula One driver, yes they have an option obviously they can execute whenever they want but I will play an important role and will also decide it, it will not all be about them."
Sainz, who currently sits 12th in the driver standings having scored 30 points so far in 2016, hopes that Toro Rosso can provide a competitive package next year for him to be able to score strong results in order to impress Red Bull.
"I am pushing them, we are pushing all together, because I really want to have a competitive car next year with a competitive package, a competitive power unit, to be able to do some strong races and strong results, to be able to give first of all Red Bull a good image. I think it's also good for Red Bull if Toro Rosso is higher up the grid than we are at the moment and to be able to be that fifth team.
"We believe we have a car that could have been able to do it this year but not the package, we will be able to have the package to be ready to fight for points next year in all races and through the whole year. A lot of people will be looking to take a step up and I would like to be at the top of that list."