The 10-year-old tan and white Staffordshire Bull Terrier, named as ‘X’, was found by a dog walker who was walking on a pathway through scrubland by Bruntcliffe Road in Morley at lunchtime on Wednesday, January 11.
Officers are now appealing for anyone with information about where the dog came from to contact the RSPCA as soon as possible.
Inspector Kris Walker said: “This poor dog was so thin he looked like a skeleton. The lady that found him was understandably very upset.
“A vet that later examined him thought he had been dead for around 48 hours when he was found - so we think his poor frail body was dumped there after he died.
“This poor dog had clearly been neglected and starved. The poor boy would’ve suffered a lot. It is just heartbreaking.”
Anyone with information is urged to contact the RSPCA Inspector Appeal Line on 0300 123 8018.