Red Bull have extended their deadline in their search for a new engine partner, but one thing is clear: they won't use Renault power units next year.

The Milton Keynes-based squad had a public fallout with Renault as the French manufacturer has struggled to provide them, as well as Toro Rosso, with fast and reliable engines the past two seasons.

On the back of that, Red Bull owner Dietrich Mateschitz announced earlier this year that he will pull his teams out of the sport if they can't find a suitable replacement.

They have held discussions with Mercedes, Ferrari and Honda, but nothing came of it and there were also reports that they could actually go back to Renault with team principal Christian Horner admitting he can't rule anything out.

However, Mateschitz has now made it clear that there is no going back to the French company with Speedweek confirming that 'Red Bull Technology terminated the 2016 contract with Renault in September because of hopelessness'.

The in-house magazine adds: 'The reasons have been clear for half a year. Renault are not willing and able to develop a reliable and competitive power unit,' the publication states.

'Even after two years of development it lacks around 80hp to the Mercedes and its reliability is of pitiful proportions.

'The disappointment with the performance and the posturing of the French are huge. Instead of improving after the 2014 season, Renault has further fallen behind Mercedes'.

Honda is also a no-go as 'firstly Ron Dennis has insisted on an exclusive deal and secondly Red Bull would probably come off worse if they switched from Renault'.

That leaves Mercedes and Ferrari and Mateschitz once again said the powerhouses are worried strengthening a rival.

"The factory racing teams fear us and know that we are faster than their factory team," he told Speedweek.

As for their initial deadline of October, he added: "We have had to extend our deadline for two or three weeks. But there is not a competitive engine for us anyway."