Amid the complex McLaren-Renault-Toro Rosso-Honda negotiations, one part of the equation is STR's driver Carlos Sainz.

Even before the engine supply issue, the works Renault team was enquiring about the young Spaniard's availability to pair alongside Nico Hulkenberg next year (and possibly even for the last few races of this season).

Red Bull took up another one-year option on him in Austria this year - leading him to voice his frustration at not being able to pursue opportunities outside the Red Bull family that has backed his career to date.

He felt that a fourth consecutive year in the junior team, with no vacancies opening up at the senior team, where Daniel Ricciardo and Max Verstappen were locked in, could potentially stall his F1 career.

There was, however, an understanding that Red Bull would release him if one of the top teams came calling. When Renault expressed its interest, Red Bull insisted he was not available.

However, now that the financial implications of the possible Honda deal are fed into the equation, Renault have more leverage.

As part-compensation for surrendering its supply of engines to the junior team to facilitate any possible Honda switch, Sainz is a possible pawn in the game.

If Renault agrees to swap its contracted supply from Toro Rosso to McLaren - and thereby facilitating Toro Rosso a lucrative agreement with Honda - then could Renault have Sainz as part of that deal? That essentially is Renault's negotiating position.

Renault chiefs Cyril Abiteboul, Jerome Stoll and Alain Prost, along with F1 managing director Ross Brawn, leave McLaren’s motorhome in Monza amidst speculation that they could be the Woking outfits engine suppliers next season Renault chiefs Cyril Abiteboul, Jerome Stoll and Alain Prost, along with F1 managing director Ross Brawn, leave McLaren’s motorhome in Monza amidst speculation that they could be the Woking outfits engine suppliers next season

Sources close to both Red Bull and Renault say that this has been agreed in principle, should the engine swap happen, but that the precise contractual terms are yet to be nailed down.

So would Sainz remain a long-term Red Bull-contracted driver simply loaned out to Renault for one or two seasons, and what financial adjustments would be made and by whom?

The contract duration could be a crucial consideration for Sainz.

The contracts of both Ricciardo and Verstappen in the senior team run until the end of next season. What if one, or both, should leave?

It would be ironic that, having waited in vain for four years for a Red Bull opportunity, Sainz should be unavailable if a vacancy arose there.

Red Bull, having invested in Sainz, will absolutely want him available to return should he be needed as a Ricciardo or Verstappen replacement. Would Renault be prepared to live with that?

The other implication in this whole business is that Renault's focusing on Sainz suggests that neither Fernando Alonso nor Robert Kubica are figuring as serious candidates as Hulkenberg's team-mate for 2018.