The Scottish SPCA is now appealing for information after the animal was found in South Lanarkshire suffering and in pain.
Scotland's animal welfare charity was alerted on Monday by the local dog warden after a member of the public found the elderly female dog wandering in Libberton, near Biggar, South Lanarkshire, at the weekend.
The dog warden took the spaniel-type crossbreed to a vet, who assessed that she was in extreme pain and the only humane option was to put her to sleep to end her suffering.
The Scottish SPCA is now appealing for help to trace her owner.
Inspector Gillian Dick said: "We were alerted to this poor dog's plight on Monday after she had been assessed by the vet, who has provided us with a statement which certifies that she has been caused prolonged, unnecessary suffering as a result of the untreated open wounds found on her underside which appeared to be abscesses that had burst.
"We've no doubt this little dog would have been in a great deal of pain and, although it is incredibly sad that she could not be saved, we are glad she was found when she was and prevented from enduring any further suffering.
"It's important we find out how this poor girl came to be found in this way so we are asking anyone who recognises her to contact us on 03000 999 999."
Anyone found guilty of causing an animal unnecessary suffering can expect to be banned from keeping animals for a fixed period or life.
The Scottish SPCA is Scotland's animal welfare charity and is separate from the RSPCA, which works in England and Wales.
The organisation is the only animal charity in the UK able to report animal cruelty cases to the Crown, with reports sent to the Crown Office and Procurator Fiscal Service.
The Scottish SPCA receives no government or lottery funding and has a policy of not putting healthy animals to sleep.
In 2012, the Scottish SPCA animal helpline received 195,299 calls and 55 people were banned from keeping animals in 2012 following investigations.