The Ferrari driver had been linked with a host of teams since the shock pre-season announcement that he would be replaced next season by seven-time world champion Lewis Hamilton.
Williams had long been considered the favorites to sign the Spaniard, with team principal James Vowles making no secret of his admiration for the three-time race winner.
Audi given 'vote of no confidence'
Alpine and Audi - who will replace Sauber on the grid in 2026 - were also believed to be in the mix for Sainz's signature, with reports indicating the 29-year-old had already rejected an offer with the latter earlier this season.
Now, F1 pundit Craig Slater has now revealed that Sainz may have been 'turned off' signing for the German manufacturer given their struggles to be ready for their introduction to the sport.
Speaking on the Sky Sports F1 Podcast, Slater said: “I think is was a vote of no confidence for Sauber/Audi, chiefly when you think about the family connection with Sainz and Carlos Sainz Sr winning Dakar with Audi and the Volkswagen Group.
“For him to walk away from that when it seemed the most obvious place for him to go is a clear sign that things are not right there.
“I spoke to someone who has a good window on what the goings on are like currently at that team.
“He’s not saying anything which isn’t obvious, but he described it to me as a mess and observed that this is a team that can’t even put a wheel on a car properly at the moment.
“So the turmoil at the top is reflective of things going badly wrong at the moment.”
“So I think all of that has been a turn-off for Sainz. I think he is worried if he goes there, he’s in the kind of situation that [Valtteri] Bottas and Zhou are in [at Sauber] - not much better next year - and who is to say what happens the year after that as well," Slater added.
“I think in a way that he has chosen the best option available to him. And yes, I think someone as logical and as practical and pragmatic as Sainz and it’s a shame that he’s kind of in this position, I can’t quite understand that.
“But all his driver moves have made sense at the time, it’s just they’ve all not worked out correctly. I think he will look James Vowles in the eye and be convinced by him."