BMW Sauber's performance in Monaco fell well below the team's expectations, according to motorsport director Mario Theissen.
Nick Heidfeld could only manage a lapped 11th place in Sunday's race, while his teammate Robert Kubica retired with brake problems.
But, after both cars failed even to make it into Q2 on Saturday, Theissen said that improvements must be made, and quickly.
"A better result was not possible for us here this weekend," he said. "At no point was our car competitive. No points are the result. We have to improve our speed of development significantly in order to match our own expectations."
German driver Heidfeld complained that his pace suffered hugely once he changed onto the super-soft tires at his only pit stop, before which he had progressed as high as the fringes of the top 10.
"I was on a one stop strategy, and with the softer compound on the second stint I had degradation. We gave everything today but we were too slow here," he said.