Police investigating a violent pub brawl that claimed the life of a teenage footballer have released CCTV images of a man they want to speak to about the incident.

Patrick Cronin, 19, died in hospital on Monday, less than 48 hours after he was allegedly punched in the head in a group fight outside a Diamond Creek pub.

The devastated family of Mr Cronin issued a statement to say that they had "just said goodbye to our beautiful boy".

The statement was signed by Mr Cronin's mother Robyn, father Matt, sister Emma and brother Lucas.

"We have been overwhelmed with the love our son, and brother, has been shown and it proves to us that he has touched so many people with his wonderful nature," they said.

Patrick Cronin Photo: Supplied

Mr Cronin had been on life support after suffering a critical head injury during a fight outside The Windy Mile bar in Diamond Creek at 11pm on Saturday.

"As with his whole life he has put others ahead of himself and leaves us an absolute hero and star. We take some comfort in the knowledge that Pat was able to donate his organs and help others in need," Mr Cronin's family said.

"Our hearts are broken but he will forever be in our hearts and he will be the one to get us through this.

"All our love forever Pat."

Just hours after Mr Cronin's life support was switched off, Victoria Police released grainy CCTV images of a man they want to speak to in relation to the alleged assault.He is described as Caucasian with a solid build, dark hair and a tattoo on his right bicep and upper arm.

On the night, he was wearing a light coloured t-shirt with blue sleeves with a pocket on the front, dark pants and dark shoes.

A man police wish to speak to in relation to the brawl outside a Diamond Creek pub. Photo: Supplied: Victoria Police

"Police would also like to speak to all patrons who were present at the hotel on Saturday evening and encourage anyone who hasn't spoken with detectives to ring Crime Stoppers," police spokeswoman Julie-Anne Newman said.

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Police released an image of a man they would like to speak to. Photo: Police Media

Lower Plenty Football Club president Grant Barden told Fairfax Media that all of Mr Cronin's organs will be donated except for his heart.

"That's the only positive," Mr Barden, who has known the family for 15 years, said.

"So someone today has got some really good news...That's absolutely typical of that family."

Mr Barden said Mr Cronin had stepped in to try to drag a friend who was "basically being trampled" out of harms way from a mob that were brawling at the Windy Mile pub.

Lower Plenty football club president Grant Barden. Photo: Joe Armao

He said Mr Cronin was punched, but did not fall to the ground.

He walked back to a house in Happy Valley Rise with friends but later began vomiting and slipping in and out of consciousness before an ambulance was called, Mr Barden said.

He said when he visited him in hospital on Sunday, he didn't have a mark on his face.

"[We thought] surely he's alright. We were in hospital yesterday looking at him in bed thinking 'Come on mate' surely he'll come good, but he's not going to come good," Mr Barden said.

He said Mr Cronin's life had been stolen from him.

"You think when you're involved in a footy club you've got a lot of young men who are by nature risk-takers," he said.

"But never him ...To have it so senselessly done like this to a totally innocent bystander makes it 10 times worse because you can't reconcile it," he said.

Players family and friends of Patrick Cronin at the Lower Plenty football club on Monday.

Mr Cronin played his third seniors game for Lower Plenty - the first for the season and the first with his brother Lucas.

Mr Barden said Mr Cronin was probably the only player who could have held his head high in the side's 101-point loss to West Preston-Lakeside.

Teammates and friends of the teenager gathered at Lower Plenty's grounds for an impromptu tribute.

The group of at least 30 released balloons in the club's colours into the sky at midday on Monday.

Mr Barden spoke briefly to the group, telling to them to look after one another.

Player-coach Michael Ryan said he could still picture Mr Cronin playing on Saturday and high-fiving him after the game.

"What a buzz it was for him to play his first seniors game with his brother," he said.

"I know that's something Lucas and the rest of the family will treasure forever."

Captain Darcy Barden, the son of the club president, said he wished that 21 other "Paddys" had been running out on the ground every weekend.

Police arrive at The Windy Mile Hotel in Diamond Creek. Photo: Joe Armao

Homicide Squad detectives are investigating the circumstances of Saturday night's brawl and how Mr Cronin sustained his fatal injury.

A woman at the house where Mr Cronin collapsed said she was asleep when he came home with friends. She did not want to be identified.

The Windy Mile - the bar where the brawl took place - did not return phone calls made on Sunday, but staff posted on its Facebook page: "The Windy Mile Team are devastated - our heartfelt thoughts and prayers go out to Patrick and his family and friends at this very difficult time. In light of these circumstances we will remain closed today and tomorrow."

Anyone with information is urged to call Crime Stoppers at 1800 333 000.