Robert Kubica admits he faces a near "impossible" task to maintain his title challenge if the pace of the BMW Sauber does not improve in the second half of the season.
The Pole raced to his maiden grand prix win in Canada last month - a victory that took him to the top of the drivers' championship - but suffered a harsh reality check in France last time out, qualifying just seventh and finishing fifth.
There was certainly an element of good fortune in Kubica's Montreal victory, notably Lewis Hamilton and Kimi Raikkonen's infamous pit lane tangle that eliminated both drivers, but the BMW was at least up with the pace.
In France, however, the Hinwil-based team slipped off the speed of both Ferrari and McLaren, while the likes of Red Bull Racing and Renault appeared to have closed the gap and Toyota had nosed ahead.
"People saw the results from Canada and thought we were the strongest, but we knew in Mangy-Cours it would be impossible to repeat this result," said Kubica.
"We were not competitive compared to Ferrari and McLaren but also some teams were in front of us, like Toyota, so we have to improve."
"Ferrari and McLaren are in front of us a bit more than they were at the beginning of the season. Now it becomes more difficult.
"It looks like especially Ferrari, and also McLaren, have gone forward more than us."
"In the end the championship depends on many factors, but to fight for the championship when your pace is half a second slower than the top teams, then it's really difficult, or even impossible."
"But everything can change, and maybe we'll get some upgrades and developments on the car that will improve our pace and everything will become easier."
Kubica's French woes saw him relinquish the lead in the drivers' title to Ferrari's Felipe Massa, who eased to victory after Raikkonen slowed with a damaged exhaust when leading.
The 23-year-old trails Massa by just two points ahead of this weekend's British Grand Prix - the midway point of the season - but he concedes the title is an unrealistic target.
"In the end you are racing for the championship," he continued. "I don't think I will be able to win it, but you can always try."
Looking ahead to the race at Silverstone this weekend, Kubica revealed he expects the BMW to have clawed back some of the pace lost to the mid-field runners last time out.
"We have made some changes to the car and I think we will come back to the normal situation," he said.
"We're hoping for a better performance, but still I'm expecting quite a big gap to Ferrari and McLaren."