Sauber is still investigating whether or not something broke on Sergio Perez's car after the Mexican hit the wall through the Swimming Pool section at the start of Q1, rendering him at the back of the grid without a qualifying time.
Perez, who finished second in the Malaysian Grand Prix, has shown good pace in Monaco practice and this proved the first time that he had been bumped out of qualifying at the first stage in 2012.
"I am disappointed as I felt we could fight for a very good grid position here," he said. "We are still analyzing everything to see if there was something wrong with the car.
"I was on my first lap, so was not pushing a lot. I went into the tunnel and had a lot of understeer and then I went into Turns 13 and 14. Thirteen was quite fine but in 14 I just went straight and didn't get the car to turn."
Teammate Kamui Kobayashi also made brief contact with the barriers but continued, though he failed to make Q3, placing 12th.
"Of course I had hoped for a better result today," said the Japanese. "With the super soft tyre compound you only have one lap to set a good time. I managed to improve in Q2, but unfortunately not enough to be able to start in Q3.
"Nevertheless, the car was good and it will be good in the race, so I think we can improve tomorrow. A lot will also depend on our race strategy and some luck in terms of safety car periods, which can always happen here. I'm positive we can score good points tomorrow."