The animal was found deceased in a resident's garden in Rosebank Avenue, Blantyre, on Wednesday, 16 December.
It was reported to the SSPCA who are treating the death as suspicious.
The charity is appealing for information and has reminded members of the public that foxes are wild animals and should be left alone.
Scottish SPCA inspector, Sian Robertson, said, “The fox was found wearing what looks like a collar of some sort as if someone has put it on the fox.
“Although it can’t be proven, it seems as if someone has possibly put this round the fox’s neck- perhaps when it was a cub.
“The injury is very similar to that of a cat which has caught its front leg through its collar, and the friction then causes a wound.
“The subsequent injury inflicted on the fox due to the collar is horrific and would have caused the fox significant pain and suffering.
“We would urge the public to remember that foxes are wild animals and should be left alone and admired from a distance unless they are visibly injured or in distress, in which case the public should call our animal helpline.
“If anyone has any information on how the fox came to be in that situation, we would urge them to phone our helpline on 03000 999 999. All calls can be treated confidentially.”