A gang used a pit bull terrier as a weapon to attack a man in Salford.
The 41-year-old was walking his dog in a field off Bolton Road in Pendlebury when he was confronted by three men on 8 June.
They threatened him and demanded he hand over his pet and, when he refused, set their dog on him.
The animal, described as a large brown pit bull, tore the man's jacket. He escaped after throwing some cash on the ground and running away.
Greater Manchester Police described it as an unprovoked attack and urged any witnesses to come forward.
Det Sgt Roger Smethurst said: "This is quite an unusual attack where a dog has been effectively used as a weapon by its owners.
"We have all seen the devastating consequences when animals attack people, and thankfully the man was not seriously injured.
"What I want to stress is that it is the handlers of the dog who are to blame, not the dog itself, and we need to catch these men.
"They have bred a dog ready to obey their violent commands, which in itself is a form of cruelty, and have manipulated this dog to attack someone else."
The man handling the dog was white, about 5ft 10in (1.77m) tall and aged between 25 and 30. He was wearing a black hooded top and tracksuit bottoms.
The other men were also white, aged between 25 and 30, and wearing black hooded tops and blue jeans.