The puppy, named Pumpkin by RSPCA staff, was discovered abandoned in woodland in Kirkham.
A member of the public was walking along a footpath through a wooded area off Station Road when they found the frightened German shepherd puppy.
RSPCA inspector Amy McIntosh, investigating, said: “The walker was very worried about her as she appeared to be alone, was staggering around and couldn’t walk properly so they rushed her into a veterinary surgery nearby.
“She was very thin and extremely weak and she’d been left out in the cold on her own. We don’t believe she had been there for long as it is a busy dog-walking area and we think she would have been spotted out in the open fairly quickly so we suspect she was abandoned there shortly before 3pm.
“She wasn’t tied up and didn’t have any belongings or bedding with her so it looks as though she’s just been plonked there without a second thought.
“She was completely emaciated, dehydrated and very, very weak.”
The poorly pup, thought to be between four and six-weeks-old, was rushed to the vets for emergency treatment.
Sadly, her test results showed she was anaemic, riddled with parasites and was suffering with serious liver problems. Vets decided the kindest thing to do was to put her to sleep to prevent further suffering.
“I’m devastated that Pumpkin couldn’t be saved and furious that someone could abandon such a weak, vulnerable puppy and leave her to die,” inspector McIntosh added.
“I’d like to urge anybody who recognises her or who may know where she came from to get in touch with me by calling 0300 123 8018 and leaving me a message.
“It’s completely unacceptable to dump her like this. She’s been cast aside just like a broken washing machine or an old mattress. There is no excuse for this sort of irresponsible and mindless cruelty.”