Wet clutch pedal

2004 TD5.
My car has been stood for a couple of days. Went out to it this morning and there is a wet patch on the driver's rubber mat under the clutch pedal.

The pedal is wet and the liquid has an oily feel. Any suggestions on what this might be and where to start looking

Thanks Neil

I would head straight to the clutch master cylinder, do not pass go and do not collect £200