The FW25 has failed to deliver so far this season
BMW's motorsport director Gerhard Berger has written off the Williams team's chances of challenging for the world championship this season.
The engines supplied by BMW to Williams are widely believed to be the most powerful in Formula One.
And BMW is disappointed that the new Williams FW25 car has failed to live up to expectations in 2003.
BMW's contract with Williams runs out at the end of 2004 and talks about extending it have dragged on well past the initial deadline.
"BMW has been building the best engines for several seasons now," said Berger.
"But unfortunately we are lacking on the aerodynamic side.
If you have any problems with a partner you have to support them
"This means we may win one or two races, where our super engine will help, but the world championship will probably remain a dream this season.
"We are far away from the aims we had before the season started.
"But if you have any problems with a partner you have to support them and help them to get back to the old level of performance."
While rivals Ferrari and McLaren delayed the launch of their new cars, Williams had the FW25 ready for the start of the season.
Team boss Sir Frank Williams admitted on the eve of the new campaign that there were still aerodynamic problems to iron out.
But Berger's comments contradict the view from the Williams camp that the car has the potential to challenge later in the season.
Williams are fourth in the constructors' standings behind McLaren, Ferrari and Renault, and have failed to win a race since the Malaysian Grand Prix in March 2002.
BMW's other motorsport director Mario Theissen has said, however, that the company is keen to remain in F1 beyond 2004.
And Berger insists Williams are in a strong position to clinch an extended engine deal.
"We're still negotiating with Williams F1," he said. "It's the first option and they are in pole position."