The impressive Spaniard has often been linked with a departure from Toro Rosso, but until now Red Bull has insisted he honour his contract until 2019.
But when asked about the 22-year-old, McLaren boss Eric Boullier said in Baku: “I know him and I like him.
“Everyone in this paddock is an option,” he told Spain’s AS newspaper.
Stoffel Vandoorne is under contract at McLaren for 2018, but speculation is rife that Fernando Alonso will depart.
Boullier admitted Sainz’s existing contract could be an issue.
“You have to look at the contracts and if he is free, but I like Carlos and he’s an option, yes,” said the Frenchman.
“Saying that, we want to keep Fernando and we hope he continues with us, to be the champion we want, and we also believe in Stoffel,” he added. “Those are our real options.”