A four-year-old boy was left with a fractured skull and part of his ear hanging off after he was battered with a brick on wasteland near his home.
The boy was attacked on land behind Danes Drive, Hessle
Charlie Davis was found by a couple walking in the area in Hessle, near Hull, East Yorkshire, on Thursday.
He was taken to Hull Royal Infirmary where he had surgery to repair his ear, and was released on Saturday evening.
The attack is thought to have happened just before midday on Thursday, after Charlie went to play with a friend.
A Humberside Police spokeswoman said: "This little boy has suffered a nasty attack and has some horrible injuries."
A scan showed Charlie's brain was not injured in the attack, which happened about 200 metres from his Danes Drive home, on a strip of wasteland next to Station Road close to the Hull-Hessle railway line.
The police spokeswoman said officers were following a number of lines of inquiry to work out what had happened.
"There has been information suggesting possible suspects and these form one of the lines of inquiry being pursued," she said.
'Might have been chased'
There have been reports that Charlie was snatched by a local youth, pulled along a path and tied to a tree before being battered.
But police said there was no evidence to confirm reports he was abducted or tied up.
The spokeswoman said: "It is currently unclear how the child got to the area. He may have gone of his own accord, he might have been chased there or he may have been taken by someone against his will."
She said officers had not spoken to the child so far, and a specially trained officer would take his statement.
Statements had been taken from his parents and other witnesses.
"We do understand that the victim was struck with a brick which has resulted in his injuries," the spokeswoman said.
"But, clearly, until police can get an account from the four-year-old victim it is not possible to confirm any more details of the incident."