The Dewsbury Neighbourhood Policing Team would like to speak to anyone who saw or has information about an incident on Ellis playing fields, off Healds Road, on April 4.
It took place at about 2,30pm after the victim, a 79-year-old man, was approached by the dog off its lead as he walked through the fields.
The dog bit the man on his torso and leg before it was then retrieved by his owner who left with the animal.
The victim later had hospital treatment for the wounds.
A number of enquiries have been ongoing to identify the owner, who was described as around 5ft 8in tall, scruffy and dressed in a tracksuit, trainers and hooded top with the hood up.
The dog was described as a bulldog type animal.
Anyone who saw the incident, who recognises the description of the animal and owner, or who has information is asked to contact the Dewsbury NPT on 101 referencing crime number 13220182080.
Information can also be given online at www.westyorkshire.police.uk/101livechat or anonymously to the independent Crimestoppers charity on 0800 555111.