That is the claim of Josep Viaplana, the F1 correspondent for the Spanish sports daily Diario Sport.
“Sainz is among the drivers who have made the most progress in recent seasons, despite his modest Renault-powered Toro Rosso,” he said.
Earlier, Spaniard Sainz, 22, had been linked with a move to Renault or Ferrari, but until now Red Bull has not been willing to relinquish his contract.
Viaplana added: “Red Bull knows he (Sainz) cannot stay a fourth year in Toro Rosso.
“Helmut Marko and Christian Horner have already decided that if Ricciardo and Verstappen stay at Red Bull Racing, they will open the door for Sainz to look at a better option.”