Carlos Sainz has signed a deal to join Renault and trigger a series of domino changes that will secure McLaren the French car manufacturer's engines for 2018, Autosport has learned.
While news of McLaren's progress in its efforts to switch from Honda engines has not been forthcoming in public, behind-the-scenes developments have been taking place that appear to show it has succeeded.
High level sources have confirmed that Sainz's deal has been agreed as part of a sweetener for Renault to end its Toro Rosso contract early.
With the Sainz deal arranged, that has opened the way for Toro Rosso to finalise a switch to Honda engines for next year, which in turn ensures McLaren will get hold of a supply of customer Renault power units for 2018.
After a frantic Italian Grand Prix weekend, where discussions to sort the McLaren-Honda situation were intense, it emerged that Sainz was becoming a key part of the equation.
Renault indicated that it wanted some incentive to switch its customer supply from Toro Rosso to McLaren.
With Sainz, it has a promising youngster to run alongside Nico Hulkenberg to help its efforts to move up the grid.
Although the provisional deal is for 2018, sources have suggested that Sainz could join Renault as early as this year's Malaysian Grand Prix if the outfit elects not to continue with Jolyon Palmer.
If that development happens from Sepang, then it is likely that Pierre Gasly will be given the call-up to join Daniil Kvyat at Toro Rosso.
No firm decision has been taken regarding Sainz's full-time replacement for 2018, but one contender would be Honda junior driver Nobuharu Matsushita, who will likely be released from his McLaren development driver role.
However, Matsushita does not yet have enough superlicence points to be able to race in F1, and needs to have a strong end to his 2017 Formula 2 campaign to secure third place in the championship to get the required 40 points to step up.
The Sainz-Renault deal has cleared the way for Toro Rosso to complete a switch to Honda engines, with the Faenza-based team also taking a supply of McLaren gearboxes for it to use with the Japanese company's power unit.
Once the Toro Rosso-Honda agreement has been finalised, then the final issue to be sorted will be McLaren's Renault contract - although that will then likely be a formality.
It is thought that all the deals will be completed by the start of next week to ensure that announcements can be made ahead of the Singapore Grand Prix.