Red Bull chiefs have apologised for Max Verstappen's run of disastrous car reliability in 2017.

Amid rumours that the Dutchman wants out of his 2018 contract, Verstappen has been decrying his constant technical problems, including a clutch failure in Austria.

"After a while you think 'How long can this go on?'" the 19-year-old is quoted as saying by De Telegraaf.

"I know the team is working hard and doing their best, but something else is always breaking."

When asked what his bosses Christian Horner, Dr Helmut Marko and Dietrich Mateschitz have said during this period, Verstappen answered: "What did they say?

"Sorry, sorry, sorry. That should not happen. Yes, I have told them clearly I am not happy, but I think they see that already."

Verstappen's mood combined with the unreliability has only fuelled rumours of a Ferrari switch, but Red Bull say that they have the youngster under firm contract.

"Despite the fact that there is a lot of speculation, there are no problems with our drivers," boss Horner insisted. "They're doing a fantastic job.

"I wouldn't want any other drivers in our cars."

Nonetheless, the rumours persist.

Italy's Autosprint quotes Verstappen as saying: "We have a contract and I think the team can do a good job.

"But the whole package must be able to get results and I think, at the moment, that is not the case. We can see clearly that we are not the fastest on the straight.

"It is absolutely not a good time and I am very disappointed, but it will be important to continue to push everyone forward, because there are still a lot of races."

The next race comes in the form of the British Grand Prix this weekend.