Liverpool have said fan safety is their priority as they continue to assist the investigation into the serious assault of a man before the 5-2 Champions League semifinal first leg win over Roma at Anfield.
Two men from Rome, aged 25 and 26, have been arrested on suspicion of attempted murder after a 53-year-old Liverpool fan was attacked outside the stadium shortly before kickoff.
The fan, reported to be from Ireland, was at the game with his brother and it is believed he was hit with a belt before falling to the ground.
He is being treated at Walton Neurological Centre where his condition is described as critical, Merseyside Police have said.
A JustGiving page has been set up to raise £5,000 for the man, while Liverpool -- who said they were "shocked and appalled" by what happened -- have promised full support to his family.
"Liverpool Football Club will continue to work closely with the relevant authorities to establish an understanding of the facts following a serious and disturbing incident at Anfield last night which has left a 53-year-old supporter in a critical condition in hospital," a statement said.
"The club's first priority is the safety of all fans attending matches. Supporters attending a game should never be subjected to an environment of violence or attack.
"Liverpool would like to thank the emergency services and members of its own supporter base who offered care and treatment to the stricken victim in the immediate aftermath.
"The club would again remind anyone who has relevant information that will assist Merseyside Police to make contact via the channels identified by the constabulary."
Police made nine arrests, with two of five men from Italy who were detained being questioned on suspicion of attempted murder.
One of the five was detained for affray and possession of an offensive weapon, another for possession of an offensive weapon and a third for criminal damage inside Anfield.
Four men from the UK were arrested on suspicion of assault, affray, being drunk and disorderly and possession of a class A drug.
UEFA, waiting for reports before deciding on disciplinary charges, said it was "deeply shocked by the vile attack."
"The perpetrators of this ignominious attack have no place in and around football and we trust they will be dealt with the utmost severity by the authorities," a statement said.
Roma said they condemned "in the strongest possible terms the abhorrent behaviour of a small minority of travelling fans who brought shame on the club and the vast majority of Roma's well-behaved supporters."
A statement said the club were "cooperating with Liverpool, UEFA and the authorities."
Liverpool captain Jordan Henderson posted a message on Instagram in which he wrote: "The thoughts and prayers of all the players are with the Liverpool fan who is currently very poorly in hospital after being badly hurt ahead of our game last night.
"He came to watch a football match and support our team -- the only result that matters to us now is that he recovers and can return home to be with his family and loved ones. You'll Never Walk Alone."