Not too many that kill fox for food. It would need to be a large animal.
Of course we know that carnivores do not usualy eat other carnivores for food. However, it does happen, and many other animals are capable of killing fox.

here is one that will eat one if…:

http://www.sch.im/wlp/pages/european%20 … wl%201.htm

although opportunistic, (there main prey is large rabbits and opposum).