McLaren's Jenson Button admitted he was totally at a loss to explain his poor performance in the Canadian Grand Prix.
The Englishman finished a lapped 16th as his team-mate Lewis Hamilton won.
"I'm confused and very lost," said Button, who is now 43 points behind Hamilton, who leads the championship.
"I don't have an answer. I just didn't have any pace and couldn't look after the tyres. I'm not two seconds slower than Lewis - I don't know what's going on."
The 32-year-old added that it was "probably my worst race for many, many years" and that "we have to improve it and sort it out sooner rather than later".
Button qualified 10th after suffering similar problems getting his tyres into their operating window to those he has had in the last few grands prix, but expected to make progress in the race. Instead, he went backwards.
"The last few weekends have been pretty poor anyway but every time you jump in the car you're still confident it's going to go well, and every time you make changes you think you're going to improve it," he said.
"I'm pushing the car to its limits and I'm 1.5 to two seconds off the pace of the leaders, and one is my team-mate. It's a little bit confusing.
"[It's] terrible and it seemed to get worse and worse. I couldn't look after the tyres; I didn't have any pace, there was nothing there. I don't know why."
In recent races, Button has felt the answer to his poor qualifying pace has lain in the way he works with the tyres.
But he said that Canada had changed his view on that.
"It's not tyres, I can't be the only person who can't drive the tyres," he said. "It's impossible."