A classic car that was meant to drive Lewis Hamilton around for the customary pre-race parade lap broke down and leaked oil all over the left-hand side of the grid around an hour and a half before the start.
Following a clear-up effort, large patches of cement dust were left covering the track to soak up the spillage.
And Sainz reckons the dirty track played a role in the chaotic scenes at the start as both he and Fernando Alonso suffered spins at Turn 1.
“I saw a lot of oil from the cars that we used to do the drivers parade, which is another thing for the FIA to look at, because it is not fair that all the oil was on the inside line,” the Ferrari driver said.
“Apart from the dirty track already being there, on top of that, we put cars that are leaking oil into the track one hour before the race – it’s unacceptable.
“That probably caused a lot of the crashes into Turn 1.”
Race-winner Max Verstappen admitted the oil spill was “not ideal”.
“It was a classic cars, from the driver’s parade,” the Dutchman added.
“So that’s maybe something that we have to look into because it’s a bit of a shame that happens. I had to steer bit left of it at the start.”
Pierre Gasly, who started a season’s best fourth for Alpine, believes it created unfair conditions at the start of the race.
”It wasn’t nice, especially lining up on the best spot of the year for us,” said the Frenchmen, who ultimately finished 11th.
“I’ve discussed it already with FIA, and I’m sure we’ll change a few things, because it doesn’t feel really fair that some guy’s got to start on oil and some others have clear Tarmac. I’m sure they’ll fix it.”
Mercedes’ George Russell, who started alongside Gasly in third, said: “It’s not the first time we’ve seen these historical cars dropping oil.
“It was pretty shocking to see how bad it was. But they did a good job to clear it up for the race.”