Pastor Maldonado believes Williams has now been left behind by its rivals in the Formula 1 development race and needs to work hard to catch up before the season ends.
The team qualified only 15th and 18th in Korea with Maldonado and Bruno Senna.
"It was really bad," Maldonado said. "It looked better in the morning, but we struggled in qualifying. I don't know why.
"For some reason we've missed a bit of performance. That's clear, both cars are at the back. In the past we used to be closer to Q3 and quite often in Q3 easily. Now we need to work very hard to try to introduce something to become stronger, in qualifying especially."
He reckons Williams's Korea form is a symptom of it dropping off the pace, rather than a one-off result.
"I think the other teams improved more than us. We need to work," said Maldonado.
Although Maldonado acknowledged that Williams's DRS is a weak point, he said that was not the sole factor in its Korea disappointment.
"Today what we lost was not related to the DRS, it was related to many other things," Maldonado argued. "We lost time in sector one, sector two and sector three. We struggled in general.
"I think it's general performance. We need to work very hard to be competitive again."
He promised to try and make up ground with an aggressive start, but fears he will not succeed.
"We need to go for it, try to gain some places, and then we'll see," said Maldonado. "But it will be difficult tomorrow."