When this happened to me (on an
Ibiza) it was the clutch pedal. You probably have a sheet steel pedal, not the fancy cast plastic one in the illustration above, and the master cylinder pushrod fits into the white plastic housing which fits into a little sheet steel box, folded and welded onto the side of the pedal arm. The spot weld in the base of the box has failed, allowing the master cylinder arm to push straight through, pushing the white plastic housing clip out and breaking it.
Cure is a new pedal, if you're in a hurry, or take the old one out and re-weld the little box if you have the time and the equipment. Working in the drivers footwell is hard, there isn't a lot of room - I think the Seat way is to take the drivers seat out.