The Spaniard could move to Red Bull, having left (on loan) the programme as he no longer wanted to drive for the junior team of Toro Rosso.
However, he will face competition from a current STR driver, in Pierre Gasly, who has two top six finishes to his name in 2018.
Zak Brown, McLaren’s team boss, has admitted that Sainz would be high on the list if he was a free agent for next year.
“We think Carlos is an excellent race driver,” Brown said.
“Of course Carlos is potentially on the market, we don’t know his exact situation at Renault and Red Bull, but he’s certainly someone that as you go down the shortlist of drivers you’d consider putting in a race car.
“If he was free, and if we had a seat, he would certainly be high up on the consideration set.”
The move would all depend on where Alonso and Vandoorne choose to be for 2019. The main decision for the two-time World Champion is either F1, IndyCar, WEC or retire.
“We do have a long-term agreement in place with Stoffel and Fernando, but as you can imagine in these contracts there’s a variety of elements to them,” said Brown.
“We will make our driver decision ultimately when we’re ready. I anticipate that being some time after the summer break.
“We’re still reviewing – analysing what’s ultimately the best combination for McLaren moving forward. Stoffel is very much part of that consideration set.”
However, there is a fourth man to throw into the mix as well for McLaren. What about Lando Norris?
If the Brit goes on to win the F2 Championship, he cannot drive in the series again, and would most definitely be looking for a drive in the top tier of single-seater racing.
Norris has said, though, that staying at McLaren would be the “perfect situation” for his career at this point.
“We think Lando is obviously a future star. We’re going through our whole driver scenario, and when you have a talent like Lando, you want to keep them in the family,” Brown said.
“I wouldn’t say it was as black and white [compared] to what’s been reported.”