Sainz remains part of the Red Bull camp despite being released as part of the negotiations to get Toro Rosso out of what was a firm 2018 engine contract with Renault.
He has been loaned to Renault for next season, meaning the Enstone team and Red Bull are keeping their options open for the longer term.
The appeal of Sainz to Renault is obvious. The team gets one of the most promising young drivers in grand prix racing. Forming a potent combination with Nico Hulkenberg as the team strives to move up the leaderboard in its third season with full Renault backing.
For 2019, when Renault will potentially be closer to the front and thus attractive to even the top drivers. Tthe team would still have a free seat. Sainz may well stay, but the other possibility is he is recalled by Red Bull to drive for its senior team.
Daniel Ricciardo is out of contract at the end of 2018. While Max Verstappen is understood to have an option in his 2019 deal. That allows him to leave Red Bull should it underperform next season. Both have huge appeal to rival teams.
Kimi Raikkonen’s deal at Ferrari has only been extended for one season. While Mercedes currently has no drivers signed for 2019. (although in the coming weeks Lewis Hamilton and Valtteri Bottas could both extend their contracts into that season or beyond).
Verstappen is losing patience with Red Bull-Renault, and while Ricciardo also wants a car with which he can win regularly. Both will want to know about the team’s future engine plans. As the possibility is there to join Toro Rosso and switch to Honda in 2019.
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If either leaves Red Bull, Sainz can slot in.
The likely replacement for Sainz at Toro Rosso next season (and maybe sooner) is Pierre Gasly. Although out of favor for a while. The Frenchman won the GP2 title last year and has done an excellent job in Super Formula in 2017, winning two races in a row.
With the Renault deal now all-but-confirmed, Fernando Alonso can extend his stay at McLaren.
It’s understood he hasn’t done so yet, and one could surmise that money is a sticking point. As Honda won’t be around to pay the sort of salary he’s enjoyed for the past three seasons.
McLaren-Renault has obvious appeal, but only if he can be confident that the 2018 car will be as strong as Red Bull’s and capable of challenging for podiums.
The likelihood is he will only sign for one season, keeping his options open for 2019 and beyond. But who would go to McLaren in the unlikely event that Alonso decides not to stay in 2018?