Jenson Button blamed a misunderstanding between himself and his McLaren team for his failure to make it into Q3 during qualifying for the Belgian Grand Prix at Spa.
The Briton will start 13th on the grid after he was bumped in the final stages of Q2, having slowed to cool his intermediate tyres before going for a final run - not realising that he didn't have enough time to complete another lap.
"Misunderstanding," he said. "I obviously did my first lap and then I cooled the tires not knowing that I didn't have any more laps left and obviously the track was getting drier and drier every lap.
"There were so many cars out there so... I think I was second or third quickest when I did my lap. I didn't get the opportunity to do another lap so... wow. That's massively disappointing and a big shock because obviously in Q1 I was a second quicker than anyone. So a misunderstanding and a mistake on our part."
Button dismissed suggestions that moving over to free up his teammate Lewis Hamilton, who was on a hot lap, had any impact on his failure to make it around the circuit in time to complete another lap.
"I did it because that was my cool-down lap," he said. "I didn't realize that was it otherwise obviously I would have kept pushing. I didn't realise I didn't have another lap.
Button said his disappointment had been compounded by the apparent competitiveness of the McLaren MP4-12 in race conditions, adding that he believed he would have had a shot at a front row start on Sunday.
"I had a completely dry setup," he said. "But our car is very quick around here and every practice session we have been in the top three so it has been very competitive. So it's tough being back in 13th. But we have got to deal with it now.
"To try and win the race from where we are is pretty much very, very difficult so we will see. It would be a lot easier from the front row. I didn't expect to be 13th on the grid and we wouldn't have been for this misunderstanding.
"Massive surprise. Going to go back to the motorhome and have a cup of tea. No point thinking about it anymore, we made a mistake and that's it. Got to move forward now. But starting 13th and we have the quickest car out there basically. It's tough."