Lewis Hamilton claims his Mercedes W08 is suffering from "some really big problems" and is not the best car in the Formula One field after he had to settle for second behind Max Verstappen at the Malaysian Grand Prix.
The three-time world champion began the race on pole at Sepang but could not prevent the Red Bull youngster from claiming the chequered flag, while title rival Sebastian Vettel recovered from starting at the back of the grid to finish fourth.
Hamilton did extend his lead in the drivers' standings to 34 points from Ferrari's Vettel, but the 32-year-old cut a downcast figure when he addressed the media after the race.
"There is a lot of work for us to do," he said.
"But there's nothing we can do, it's the way the car is.
"People have been saying all year long that we've got the best car. It's a fact at some races that the car has turned out to be better but overall, globally, I think it's worked out that we've not got the best car.
"We've done an exceptional job with what we have. There are some really big problems which I can't really explain to you what they are but we really need to make sure we rectify them for next year's cars if we really want to fight both Ferrari and Red Bull when they step up their game."
There are five races remaining this season, with the Japanese Grand Prix at Suzuka coming up next weekend, although Hamilton claims to be uncertain where the Mercedes will perform best over the climax to the campaign.
"I don't know which one of these next races are going to be good for us but we'll do everything we can to try and stay ahead," he said.
Mercedes' chief Toto Wolff shared the concerns of Hamilton and urged the team to retain their composure as they seek to rectify the deficit in pace during the weeks ahead.
"I'm very down," Wolff told Sky Sports. "You cannot look at it and say we have scored more points than Ferrari - we have lost so much pace this weekend.
"We were half a second down on Ferrari [per lap] and probably if Max had pushed to the end we would have been half a second down on Max.
"How can a car that is so fast on many circuits lose so much with the tyre that is overheating?
"In Singapore we were really good in the wet. At the moment it is about keeping calm and trying to analyse it."