Foxes injure themselves all the time, they climb trees and jump on peoples sheds it's when they jump down they injure themselves, but most of the time the injuries clear up by themselves,your little fox isn't probably injured badly, just get in touch with fox welfare people, there are plenty of fox organisations on the internet, I've been feeding our local foxes for some years now and I've seen many of them limping and walking on three legs but within a few days they're okay again.In fact I've got a semi tame vixen who waits for my car every night, (I think she knows the sound of it) anyway a week ago she came over walking on 3 legs whch worried me a bit but last night she came out of the wood walking on all 4 legs so I wouldn't worry too much but to put your mind at rest just get in touch with a fox welfare society for some advice. Thankyou for caring, I wish there were more people like you about, after all foxes have feelings too and feel pain. x