But Sainz, 23, is confirming nothing.
"Maybe I have the same information as you," he told Spanish radio Cadena Cope ahead of the Singapore grand prix.
"Already from June, after clarifying a number of things in a clear and direct conversation with them, I left my future in the hands of Red Bull.
"From then I have not done anything except wait and trust what they decide," Sainz added.
He denied that his future is inextricably tied up with the McLaren-Honda split, as McLaren and Toro Rosso swap engine partners for 2018.
"It would seem to be good if (Fernando) Alonso goes with McLaren-Renault, but what McLaren and Renault do doesn't affect me much," said Sainz.
"I'm only thinking about my weekend in Singapore."