Toto Wolff said Mercedes had delivered an "inexcusable performance" with their car in the Sao Paulo Grand Prix and that he felt sorry for Lewis Hamilton and George Russell for having to drive such a "miserable thing".
On a torrid weekend for the former champions on the circuit they claimed their last F1 win on 12 months ago, Mercedes endured a race-long struggle for pace and tyre wear in Sunday's grand prix as their wildly inconsistent 2023 car toiled around Interlagos for the second day running.
Hamilton slipped from third on the grid at a post-red flag standing start restart to eighth - 63 seconds behind race winner Max Verstappen in a 71-lap race - with Russell also unable to avoid falling backwards towards the minor points places before eventually retiring due to high power-unit oil temperatures.
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Coming off the back of far more competitive showings in the previous two events in the USA and Mexico, Mercedes' shock at what unfolded, and search for answers as to what had gone wrong, was pronounced and led to a plain-talking Wolff giving a damming assessment of the car's performance in his interview with Sky Sports after the race.
"Inexcusable performance," Wolff, Mercedes' team principal, told Sky Sports F1.
"There's even no words for that.
"That car finished second last week and the week before, and whatever we did to it was horrible.
"Lewis survived out there, but George... I can only feel for the two driving such a miserable thing.
"It shows how difficult the car is, it's on a knife's edge.
"You've got to develop that better for next year, because it can't be that within seven days you're finishing on the podium, solid, with one of the two quickest cars, and then you're nowhere and finishing eighth."
Speaking to the written press, Wolff added: "Totally baffling. At the same time, unacceptable for all of us. We are a proper structure, solid team and that didn't look like a solid team today."
Mercedes have been at a loss to pinpoint why the W14, which in the previous fortnight finished second to Verstappen on track in Austin (although Hamilton was subsequently excluded due to excessive plank wear on the underside of the car) and Mexico City, was so out of sorts in Brazil and unusually eating through its tyres.
Russell and Hamilton had already experienced a similar story in Saturday's 24-lap Sprint, when they finished fourth and seventh.
"Clearly we got something wrong this weekend," said Russell.
"Still we're not too sure what that is as yet, but the pace just hadn't been there."
Hamilton, who had described Saturday's Sprint as "horrible", added: "It didn't feel as disastrous as yesterday. Yesterday I literally had no tyres left, they were worn to zero.
"I feel like I drove a better race today in terms of managing the tyres to the best of my ability. But the car, there's like moments it works and moments it doesn't, and it's so inconsistent throughout the lap.
"So we have to figure out what that is. Then also we are really slow on the straights and sliding the car through the corners. So one to forget but hopefully there's lots of learning from today."
Wolff: 'This car doesn't deserve a win' | Brundle: 'W14 looks like it has parachute on back'
Mercedes had arrived in Brazil - where they won dominantly last year - hopeful of continuing the momentum shown since the floor upgrade was introduced onto the car, as they work towards what they admit needs to be a big step forward for 2024 to have a hope of challenging Red Bull.
But was transpired at Interlagos was what Wolff described as "the worst weekend in 13 years" for him in F1.
With the team at a loss as to why the W14 performed so badly, Wolff said it "almost drove like on three wheels and not on four".
Sky F1's Martin Brundle, meanwhile, had said during commentary that the W14 looked "like it has a parachute" attached to it such was the ease with which rivals overtook it on the straights as Hamilton and Russell started to slip backwards after initial promising starts.
Mercedes remain without a victory in 2023 with just two grands prix left and asked if the W14 deserved a win like its similarly-disappointing 2022 predecessor, Wolff starkly stated: "This car doesn't deserve a win.
"We need to push for the last two races and recover. I think that's the most important thing. And see what we can do in Las Vegas, a totally different track, and Abu Dhabi.
"But the performance today was… I'm lacking words."
Hamilton smiled and replied "thank god!" when reminded that there were just two races left of this season before the W14 could be retired from active action.
He added: "Two more races with this thing and then hopefully no more driving it."
Mercedes' last winless season was in 2011.
How did Mercedes' recent podium pace disappear?
Finding concreate answers to that question is bound to take up a lot of time in the Brackley team's immediate post-race debriefs and in the week that follows at the factory before the sport heads back to the USA for the inaugural Las Vegas GP on November 17-19.
"We are clearly not world champions on Sprint weekends," said Wolff in reference to the format in use this weekend which dictates that teams must lock in their cars' set-up for the remainder of the event after just a single one-hour practice session on Friday.
"We do some good work here on track to get it done, but still, that doesn't explain what went wrong."
It was at the last Sprint weekend at the US GP, where Mercedes introduced a new floor on to the W14, that Hamilton was disqualified for illegal skid-wear with the team later acknowledging that they did not leave enough margin on ride-height for the bumpiness of the circuit.
Speaking on Sunday, Hamilton said of the "unpredictable" W14 that Mercedes have grappled with all season: "One weekend it feels good, one session it feels good, and then not.
"I'm sure we will go and look at things and find that we should have done things differently, but with the one [practice] session it's difficult.
"I'm still proud of the team, they still came here and did their work, they hold their head up high and that's what we have to continue to do. Just keep pushing forward."
Russell agreed that the team needed to get to the bottom of the perplexing turnaround in pace.
"Twelve months ago this was our strongest race of the year, 12 months later it's by far our weakest race of the year, so very strange.
"The car was just slow this weekend. The tyres were sliding around and I think what we were doing was the maximum. Something doesn't quite add up, you just don't suddenly lose a second's worth of performance and go from a podium-fighting car to just fighting for points.
"We really need to sit down and understand, but clearly a massive one off this week."
If there was any solace for Mercedes from a chastening weekend it was that Ferrari, their rivals for second place in the Constructors' Championship, outscored them by only two points after experiencing their own problems. It leaves Mercedes holding a 20-point advantage over the Italian team with two races left.
Get ready for the big one: Formula 1 in Las Vegas! See drivers race down the Strip, and past landmarks like Caesars Palace and the Bellagio, on F1's newest street track. Watch the whole Las Vegas GP weekend live on Sky Sports F1 on November 17-19. Stream F1 on Sky Sports with NOW