The surprise winners from McLaren's engine woe

It's all change at McLaren next year, with it having succeeded in its long, drawn-out quest to switch from Honda to Renault power for 2018.

Toro Rosso will run Honda engines next year, with Red Bull in line to do the same in the future should Honda's performance improve sufficiently - potentially giving Red Bull the works-engine operation it craves.

But perhaps the most intriguing element of the intertwined deal is the news Red Bull has agreed to loan out Carlos Sainz Jr to Renault for 2018 - and what it now means for his future.

Sainz, who turned 23 earlier this month, was in an awkward position. He was part of the Red Bull family. He was given his chance in Formula 1 because Red Bull had chosen to invest in him. He has rewarded that faith, impressing since making his debut with Toro Rosso in 2015.

As a result, Red Bull wanted to keep him and protect its investment. Sainz and those around him felt he was ready to make a step up. The problem was Max Verstappen and Daniel Ricciardo have deals that keep them at Red Bull for at least next year.

Sainz had nowhere to go. He was doing all he could at Toro Rosso. Though evenly-matched in qualifying and on one-lap pace with team-mate Daniil Kvyat - the duo are the closest-matched team-mates on the grid on raw speed this season - Sainz has destroyed the Russian on a Sunday afternoon, accumulating a tally of 48 points to Kyvat's four.

He is currently ninth in the drivers' championship. That's the best position for a Toro Rosso driver since Sebastian Vettel finished the 2008 season in eighth.

But his Red Bull deal is such that he can't get out unless Red Bull says so. Sainz's frustration was growing.

In Austria, he said he was "unlikely" to stay at Toro Rosso for an unprecedented fourth season in 2018. That led to Red Bull team principal Christian Horner, Red Bull motorsport advisor Helmut Mark and Toro Rosso chief Franz Tost all questioning his loyalty.

It later emerged that Red Bull had taken up the option on his contract to keep him in house for 2018 the previous week, so its displeasure was perhaps understandable. His comment may have been a slip of the tongue but it was more evidence that he was getting itchy feet.

Moving to Renault releases Sainz from a situation that was threatening to suffocate him and ruin a career that oozed potential

Sainz did not intend to come across as being disloyal to Red Bull. He has said on countless occasions that he wants to win the world championship with the team. He recognises the investment and belief Red Bull has placed in him. But he is also an ambitious driver and there was a concern from his camp that staying at Toro Rosso for a fourth year would harm, rather than help, his future.

Tensions were cooled very quickly, with Sainz meeting with Red Bull senior management to explain his side of the story. Red Bull chiefs made it clear that they backed him. But they needed an insurance policy should Verstappen or Ricciardo leave. Sainz is the perfect fit.

Red Bull is aware that Sainz's performances have not gone unnoticed by rival teams. Sainz had an offer from the works Renault team for 2017, but Red Bull reacted by taking up its option to keep him. Renault's interest remained this year, with Red Bull once again activating the option.

But then the game changed when McLaren-Honda's relationship became untenable.

When it became clear a future works relationship with Honda was on the cards, Red Bull got involved in discussions. Marko met with Honda motorsport chief Masashi Yamamoto on several occasions. The prospect of Toro Rosso running Honda engines was discussed with Marko suggesting it would be like a trial run before Red Bull took on Honda power too.

To get the deal done, and extricate itself from Toro Rosso's contract with Renault, Red Bull has had to make a concession in the form of letting Sainz go for a year. It is believed Red Bull has an option to recall him and place him at the senior team for 2019 if it wishes. Should it decide against that, Renault can sign him. It seemingly could not have worked out much better for Sainz.

Moving to Renault releases Sainz from a situation that was threatening to suffocate him and ruin a career that oozed potential. Enstone is an impressive facility with a brilliant team of people that offers an environment where Sainz can thrive.

For the first time, he will have the might of a manufacturer - and its resources and aggressive development programme - at his disposal. It's an opportunity to kick on and prove that he has the capability to challenge for the world championship in the future.

Moving to Renault is a win-win. He swaps a Toro Rosso, which will never be allowed to beat Red Bull and will next season be powered by what is currently F1's worst engine, the Honda, for a Renault team on the up.

Renault has shown notable improvement this year, emerging with the fourth fastest car behind Mercedes, Ferrari and Red Bull. This is only its second season since returning as a full works outfit and it's nearing the end of a massive recruitment drive and complete overhaul of its Enstone facility.

As staff gel in their upgraded environment, the hope is that trajectory will steepen. It's what Sainz and Nico Hulkenberg, who also took a chance on Renault, will be banking on. But Renault continues to struggle with its engine and there's no certainty it will continue to improve in this manner on the chassis side. McLaren's threat may well increase next year, while Force India is another extremely strong presence in that part of the field.

Sainz's move to Renault might not work out. Hulkenberg will be a challenging team-mate and beating him will not be easy. He has been particularly strong in qualifying this year and will have had a year to bed into the team.

But deliver at Renault and Sainz will only enhance his reputation. He then faces the prospect of returning to Red Bull - the team with which he says he wants to win the title - or sticking with Renault, a team that appears to be on an upward trend.

And if Red Bull does not recall him and Renault turns sour, Sainz will have options to move elsewhere - this is freedom he has not known in an F1 tied to Red Bull so far.

McLaren is known to be an admirer of his, while Ferrari will be on the lookout for a partner for Vettel from 2019 onwards. Even if Charles Leclerc secures a deal with Sauber for next year and impresses, promoting him to Ferrari the following year may be considered a step too soon. Sainz would be a brilliant alternative - and a long-term one at that.

McLaren's woe is Sainz's gain. It's an exciting move for him and one that could define his career.

Sainz's release could also have finally created the circumstances for Red Bull to move junior Pierre Gasly to F1.

The 21-year-old has so far been overlooked for promotion, missing out on stepping up to F1 for 2017 despite winning last year's GP2 title.

It is believed part of the reason he missed out is that his Red Bull bosses felt he should have beaten rookie Prema team-mate Antonio Giovinazzi - now Ferrari's third driver - more convincingly to the championship.

But Sainz's departure coupled with the fact Kvyat has yet to be re-signed has opened the door once more as there are two potential seats available at Toro Rosso.

Kvyat is favourite to stay on at Toro Rosso next season to give the team some consistency but the second seat is leaning towards Gasly.

He has been in good form recently, claiming his second successive Super Formula win earlier this month to move into second overall in the championship standings. His chances are also enhanced given his relationship with Toro Rosso's new engine supplier Honda, which powers his Team Mugen outfit in Japan.

Marko and Yamamoto meet regularly to discuss Gasly's performance. And he has been lined up to replace Sainz this season, should Renault succeed in extricating Jolyon Palmer from his contract and Sainz can head for Enstone early.

While Honda-backed Formula 2 racer Nobuharu Matsushita has been linked with a seat at Toro Rosso, it is unlikely he will score enough superlicence points to be in contention.

With all that in mind, Gasly looks set to finally get his chance - another surprise big break amid the McLaren-Honda fallout to add to Sainz's.