Team boss Toto Wolff reckoned a weekend in Sao Paulo was the worst of his 13 years in F1, as Lewis Hamilton finished the GP in eighth while George Russell retired with 14 of the 71 laps remaining.
This was to protect the power unit after rising oil temperature and "worrying" pressures were detected.
Following the introduction of an updated floor for the United States GP, Mercedes initially enjoyed a jump in performance that enabled Hamilton to pressure Verstappen for victory in Austin, before being disqualified for an excessively worn plank. The seven-time champion then finished runner-up in Mexico.
The team had hoped for a similarly competitive showing in Brazil based on its race simulations in the sole practice session before realising early into the sprint race that its pace had taken a major hit.
Head of trackside performance Riccardo Musconi said: "The long run pace we showed in free practice was quite reassuring.
"We didn't think that we needed to change the car around, so we went into qualifying, and the results were around the third row. In a way, we were not pleased with it, and we felt the car deserved more."
But that promise then gave way to "alarm bells" that prompted a simulator session back at the Brackley factory after Mercedes identified concerning tyre behaviour.
Musconi continued: "The alarm bells went out during the sprint race because after the encouraging first two laps, the degradation of our car was quite high, mainly coming from the rear axle. At that stage we worried about our performance on the Sunday.
"We organised for a simulator session back at the factory, looking at the parameters we could change between Saturday and Sunday."
Given it was a sprint event with limited practice running and the early introduction of parc ferme rules, the team was restricted in how it could tweak the set-up of the W14. As such, Saturday painted a "bleak picture" of how the full GP would unfold.
"We were hoping that addressing some of the issues we experienced on Saturday, like pushing very hard on the first couple of laps, doing a bit more management and trimming a bit the balance of the car with the flap, would have been enough to put us in a more comfortable position for Sunday," added Musconi.
"What came out of Sunday was quite a bleak picture resemblant of our Saturday.
"We improved the degradation a bit on the rear axle but at the same time we started suffering from understeer, so the car was struggling to turn the corners. The pace therefore wasn't there and we couldn't compete at the front."
Mercedes clarified that breaking parc ferme rules to modify the set-up, as the expense of a pitlane start as per Aston Martin and Haas in Austin, was "off the table".
