Hi Mac, I think this Fox is suffering from what we have over here, Mange. I'm no expert, but it looks and sounds like it.
Mites burrow into the outer layer of the skin, forming tunnels into which they deposit several kinds of material (eggs, faeces, shed shell, digestive secretions) causing intense irritation to the skin. The mite life cycle lasts about two weeks and heavy infestations can build up rapidly. The disease is intensely irritating and animals have been known to chew their own tails off trying to relieve the itching. At advanced stages of the disease, infected individuals are often seen wandering around during the daytime, especially in cold weather; the infected animals try to maintain their body temperature seeking warm places, such as buildings. Death may arise from a wide variety of causes, including starvation and hypothermia. Some how I feel this one has little time left.
I think from what you have capture, it might have been wise just to let him/her just move off in their own time. Personally I would never suggest in making a noise or sound to get an animals attention, especially in this state, as it's not 'good practice', however.
Getting back to the image, perhaps moving more to the left and getting really low down on the ground may have give a better POV, as it appears the Fox was not disturbed by your presence. It also appears quite saturated in colour so I might tone that down, but watch the highlights on the LHS of the face and I would have dropped the ISO to 400 as the subject was static.
Sorry Mac, I just don't like to see animals suffering in this was, just my take.
cheers
Steve