However, Sainz is not confirming his impending move.
"Red Bull does its best for my career and so whatever they decide, I will accept it," he told Marca sports newspaper during a sponsor event at the weekend.
"It is difficult for me because what I say may please one person and displease another, so I prefer to say nothing.
"All I know is that there are many people in Toro Rosso that I want to think for making me the driver I am today," Sainz added.
"But I think for the sake of the teams involved, they are going to have to decide sooner rather than later, because (preparation for) 2018 is already here," Sainz told EFE nes agency.
The publication said Sainz, 22, had a seat fitting at Renault's Enstone factory last week.
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