The Spanish driver's current deal extends to the end of 2024, but he has stressed that he wants long-term stability and an early extension of his stay with the team.
As such, he is keen to have his future sorted out by the end of this season.
"I'm not going to lie, I don't like going into my last year of a contract without really knowing where I'm racing the next year," Sainz said in June.
"I went through that process both with Red Bull and Renault, and I know it's not ideal as an athlete, and as a driver. It's just not the right thing. And that's why I have put this winter as a reference to try and figure out my future."
Vasseur agrees that it will be preferable to sort out a deal before the end of this year.
"I think that with Carlos, we are fully aligned," said the Frenchman. "We have [been asked] many times the same question. And we always give the same reply, that we have time to discuss, that we have still 18 months of contract in front of us.
"We both want to start the next season with a clear situation. It means that we have to take action and a decision before the end of this season.
"We have still four or five months in front of us to decide. But we are fully aligned on this point with Carlos and his management, and we will have the discussion soon."
Meanwhile, Ferrari has been linked with an interest in Lewis Hamilton thanks in large part to the relationship Vasseur established with the British driver when running him in F3 and F2 at ASM and ART in 2005-6.
Hamilton has still not signed a new contract with Mercedes, despite positive noises from team boss Toto Wolff.
However, Vasseur continues to insist that despite the delay in any firm news from the Mercedes camp the seven-time world champion is not on Ferrari's radar.
"Well, I think it's the same situation with Lewis that it was the last 10 years, that they are in discussion," he said.
"I don't know what is the issue, if there is an issue or not. And honestly, I'm not focused at all on this. I'm focused on the development of the team, and the discussion is between Lewis and Toto, and not myself."
