Fernando Alonso admitted Ferrari were facing a "dangerous moment" after he qualified only 10th for the British Grand Prix.
The Spaniard enters Sunday's race at Silverstone already 36 points behind championship leader Sebastian Vettel.
"We seem to perform worse and worse," said Alonso, who won two of the first five races this year.
"We need immediately the form we had at the beginning of the year. If not, we will lose too much ground."
Alonso said Ferrari were "not happy" with their performance and said that the team were struggling with a problem that has afflicted them for several seasons - new parts not giving the performing boost expected.
"We are disappointed with today's performance," he said. "We are not delivering what we are supposed to deliver every weekend with the new parts that are coming.
"Some of them, most of them - they are not working, so we are missing a little bit of pace compared to the top teams.
"But it is hard to imagine we lose so much compared to them. If we were two or three tenths slower than the fastest car two months ago, now it is difficult to believe we are one second. So it is something more than that.
"We are not developing the car good enough, this is true, but also here in the track maybe we don't find the right set-up, the right moment. Maybe the tyres are not working effectively, whatever.
"The problem is we need to investigate it, because we must improve."
Alonso's qualifying lap was more than 1.3 seconds slower then Mercedes driver Lewis Hamilton's pole position, and 0.768secs behind Vettel, who starts third.
The 31-year-old was 0.243secs slower than Force India's Paul Di Resta and was out-qualified by Daniel Ricciardo's Toro Rosso, the second Force India of Adrian Sutil and both Lotus cars.
Lotus driver Kimi Raikkonen, who is eight points behind Alonso in the championship in eighth place starts just ahead of him in ninth position.
Alonso said: "We need to of course to be realistic about our problems in the team. But we cannot be also be too stressed about this qualifying.
"We need to improve the situation immediately, to react from tomorrow's race to next week in the Nurburgring and [two weeks after that in] Hungary.
"But in this moment we need to also remain very calm. If tomorrow we can recover some points with the leaders it will be a fantastic race.
"So we need to first finish tomorrow's race, be really calm in the factory, think what we need to do for the next two races to improve our performance."
Alonso admitted that Pirelli's choice of the hard and medium tyres for Silverstone was not ideal for Ferrari but refused to blame that for the team's lack of pace.
He said: "I don't want to complain anything about Pirelli. There were others complaining about Pirelli when they were not performing well [a reference to Red Bull].
"Now we are not performing well because the car is not performing well, because here on the track, all of us, maybe we are not doing the job well enough.
"It is true also that they are maybe not our favourite tyre choice. For us and Lotus, it is not a secret.
"But if someone with these tyres can do 1:30.2 [Vettel's qualifying time] and we cannot do it, it is our problem, so we need to improve."