Today I got confirmation from an expert about a doubtful cat that I photographed on Saturday near Dolenja vas (Senožeče - SLO). As I initially supposed it was a WILDCAT (Felis silvestris)
, roving around the snow-covered fields in the middle of the day! In the above photo you can see the very bushy tail and the clearly divided black rings around the tail (the tip of the tail being completely black). The cat was also quite big and bulky for a domestic cat and ran into cover as soon as I started watching it, after I stopped the car (yes, I spotted it while driving on a country road).
As far as I know, Wildcat is a widespread mammal across Slovenia and the area where I observed it seems quite perfect. But of course is far from easy to see one during the day.