The RSPCA has appealed for information after the three-year-old was found on the Blue Stone Heath Road in Donington-on-Bain, near Louth, by a concerned member of the public.
The dog was taken to the Black Sheep Vets on Belvoir Way, Fairfield Industrial Estate, Louth, where vet Richard Carter carried out surgery on the injured leg, but it is still severely damaged.
Mr Carter said he hopes that the leg can still be saved, but only time will tell if it will heal enough following surgery.
The amount of matted fur removed from Winnie would have been enough to have filled a supermarket bag, he said.
Mr Carter added: "This is a clear case of neglect. The matting would have taken months to have got into such a state, and the sad thing is that this could have easily been addressed.
"I cannot imagine this dog would have been able to have fended for herself for a long period of time, so therefore we can only suspect that someone has dumped her deliberately."
Mr Carter is carrying out the treatment for Winnie free of charge, and the dog is currently being cared for by a fosterer.
The RSPCA is investigating the incident, and although Winnie had been microchipped and her original owner traced, this person had since sold her on to another person.
RSPCA inspector Stuart Wainwright said: "It is just horrifying to think that she has been left to suffer for this long and then just dumped like a piece of rubbish. We are extremely grateful to Richard and his team for doing all they can to help Winnie, and we just hope now that we can find the person responsible."
Anyone with information is urged to call the RSPCA inspector appeal line on 0300 123 8018.
(This is Grimsby - August 3, 2012)