A Japanese Akita was found abandoned on a dog bed along Pietley Hill on Wednesday, August 2.
A woman driving past between 4.30pm and 5.30pm saw the dog and attempted to take it to the kennels. The dog became spooked by her and bit her as they were walking.
Another passer-by was walking their dog in the area when the Akita bit the dog.
The dog was collected by police officers and taken to a specialist shelter.
Police officer Rowen Sheppard said: “Enquiries to trace the owner of the Akita have so far proved unsuccessful. I am appealing for anyone with information about the dog or its owners to please come forward.
“I am also keen to trace the dog walker whose dog was attacked. If this was you, please get in touch.”
Anyone with information can contact the Hemel North Rural, West and Central Safer Neighbourhood Team on 101 or Crimestoppers anonymously on 0800 555 111.
You can also report information online at www.contacthertspolice.uk/Report