"At this moment, in the current Formula 1, a podium is something to dream about, it's extremely difficult," he said here on Wednesday ahead of the Brazilian Grand Prix (GP).
"Which doesn't mean that I don't try to finish as high as possible in every race, but with the system of the present Formula 1, the top three teams are very far ahead," Efe news quoted the 25-year-old Spaniard as saying.
Sainz, who reached the 100-race mark in F1 at last month's United States Grand Prix, said that his main objective for now is to be "the best of the rest".
McLaren, a team with a glorious past, has seen a dramatic improvement in results this year.
"I have to try to finish sixth, seventh, eighth, this year and try to do it again next year. It's the most we can fight for at the moment," Sainz said after taking part in a promotional event for one his sponsors, Estrella Galicia beer.
Now seventh in the driver standings with 80 points, three ahead of Pierre Gasly (Toro Rosso) and four behind Alex Albon (Red Bull), Sainz is taking nothing for granted with two races left in the 2019 season.
"Right now I'm fighting for sixth, seventh and eighth, which is not easy, because the two drivers I'm batting with have driven a Red Bull," he said, alluding to Gasly's time with Red Bull before he was shifted to Toro Rosso to make room for Albon.
"I have to keep trying to add points in these last two races," Sainz said.
The son of two-time World Rally Champion Carlos Sainz Sr. said it is "very possible" that British driver Lewis Hamilton (Mercedes), who just clinched his sixth F1 championship, will surpass Michael Schumacher's record seven titles.
Mercedes "is not going to stop winning in the next few years", Sainz Jr. said.
Asked whether taking seventh place in the final driver standings would boost his medium-term chances of being signed by one of the Big Three teams, he said: "It certainly does me no harm."
"Anyway, as you already know, I have a contract with McLaren for the coming year," Sainz said, adding that after test-driving the team's 2020 car, he does not expect the same level of year-to-year improvement as this season.
Even so, he said, "a step in the right direction will continue moving McLaren closer to the top teams, and to wait for the regulation change in 2021 for the definitive leap".
"I believe it will be a very different Formula 1, a Formula 1 that will reward the first to adapt, obviously.
"But I also believe that the budget ceiling that will be implemented in 2021 doesn't exist in 2020, nor in 2019, when the teams are developing the cars of 2021.
"I believe that for 2021, it's very probable the teams that are dominating F1 today will dominate it also in 2021," the Spanish driver added.
( With inputs from IANS )