A 30-year-old man has been attacked by two masked men who beat him with crowbars and set their pitbull-type dog on him.
The victim was assaulted in Gorton, Manchester, at about 0210 BST.
He was taken to hospital with serious head injuries and a dog bite. He remains in a serious but stable condition, police said.
A 24-year-old man has been arrested on suspicion of assault and is in police custody.
Det Con David Ogden, of Greater Manchester Police, said officers were taking the attack "extremely seriously" and urged anyone with information to contact them.