Jenson Button admitted McLaren's form was "not good enough" after a dispiriting Chinese Grand Prix.
Button and team-mate Kevin Magnussen finished 11th and 13th in Shanghai, where they had been off the pace all weekend.
"It's pretty painful out there. I don't know what we're doing," said Button.
"When you have as bad a result as this it's tough for everyone. Hopefully the team can stay positive and update the car because this isn't good enough."
McLaren are the slowest team with the Mercedes engine, which is the dominant power-unit in F1, and Button and Magnussen finished behind several cars using the less effective Renault and Ferrari engines.
Button said the car's lack of aerodynamic downforce was "a big issue".
"It's a good car, but we can't get the tyres working and that's one of the biggest issues in F1 these days." he said.
"All I know is it wasn't very quick. We start the development work now."
McLaren are planning to introduce some new parts for the next race, the Spanish Grand Prix on 9-11 May, which they hope will speed up the car by a few tenths of a second a lap.
But other teams are doing the same and Button said he doubted they would make much difference.
"We have some upgrades but we're a lot further behind than we were at the last race," Button said.
"We're maxed out on everything on the car. We're very, very high on front wing, higher than ever before. It's all very strange."
Magnussen, who is in his first F1 season and performed well after struggling in the last race in Bahrain, said: "It's a shame. We just don't have enough downforce. That's the only issue we have with the car.
"The way the car is run and how it feels is good."
McLaren remain behind Force India in the constructors' championship, after the Silverstone-based team picked up 10 more points to move onto 54 for the season.
Nico Hulkenberg finished fifth and he remains fourth in the drivers' championship ahead of the current world champion Sebastian Vettel.
"Finishing in sixth and bringing both cars home in the points again was a very positive result for the team," said the German.
Williams were also in the points as they continued to improve on last season's disappointment, despite both drivers being involved in contact on the first lap.
Valtteri Bottas, who was hit by Nico Rosberg on Lap One, finished seventh to take Williams' points tally to 36 after four races, which is already 31 more than they achieved in the whole of last season.
"It was a good race for me despite some hard contact at the start which cost me a few positions," said Bottas.
The news was no so good for team-mate Felipe Massa, who as well as having contact with Fernando Alonso on the first lap, had a problematic first pit stop when mechanics tried to replace a left rear tyre with a right one, which saw him slip from sixth place to the back of the field.
"It's a real shame for Felipe and the whole team about the pitstop and it is something that we need to investigate to ensure it doesn't happen again, as it cost us points today," said Williams head of vehicle performance Rob Smedley."