The severely emaciated pets were discovered in a property in Coatbridge, North Lanarkshire.
The Jack Russell terrier cross breed is critically ill after being found less than half its ideal weight.
A long-haired black cat, also underweight, is now in the Scottish SPCA's care after the pair were found in the town's Beechwood Drive last Thursday.
Inspector Elaine Lindsay said: "The living room door had been jammed shut so they had no access to the other rooms."
The charity is appealing for help to trace the owner. Anyone who can help should call them on 03000 999 999.