Former referees' chief: Constantine Hatzidakis' career on the line over alleged Andy Robertson elbow

The extraordinary incident occurred just after the half-time whistle was blown during Liverpool's 2-2 draw with Arsenal at Anfield on Sunday.

Sky Sports cameras zooming in on the confrontation showed Hatzidakis seemingly throwing up his arm and making contact with Robertson after being approached by the Reds full-back, who gesticulated that he had been hit by the official.

An irate Robertson was led away by team-mates but, while he received a yellow card in the aftermath, it is the action of Hatzidakis that will come under further scrutiny, with referees' body the PGMOL saying the incident will be reviewed.

Hackett, formerly head of the PGMOL, told BBC Radio Five Live: "Ultimately, if he is found guilty of this, his career is in jeopardy.

"I was trying to find an excuse as to why he did it and I came up with was he in fear? He shouldn't be, because he's in a protected environment with plenty of security.

"But he reacted in a way that he shouldn't have reacted at the end of the day and here we are talking about a match official and not a decision, but an action by a match official - and he's clearly lost his composure."

Another former top-flight referee, Mark Halsey, put the spotlight on Robertson's behaviour and believes a ban is the most likely punishment for Hatzidakis if he is proven to have committed an offence.

Writing in The Sun, Halsey drew a parallel with Fulham striker Aleksandar Mitrovic, who was recently banned for eight matches for pushing referee Chris Kavanagh.

Halsey said: "To me, it looks like Robertson goes to grab Hatzidakis, who brushes him off with his arm and catches him accidentally.

"I cannot think why an assistant would throw his arms into a player's face. Sure, from one camera angle it does not look good. But you have to ask why has Robertson gone to approach the assistant referee?

"I have heard people say this is the end of the linesman's career but, just like Aleksandar Mitrovic, it is his full-time job. However, if he is proven guilty and did intentionally use his elbow then he will face the same consequences as the Fulham frontman.

"Match officials are the guardians of standards and must be accountable if found guilty for that type of behaviour towards a player."

The PGMOL quickly issued a statement on Sunday, saying: "The PGMOL is aware of an incident involving assistant referee Constantine Hatzidakis and Liverpool defender Andrew Robertson at half-time during the Liverpool v Arsenal fixture at Anfield.

"We will review the matter in full once the game has concluded."

Liverpool boss Jurgen Klopp said he did not see what had happened, but the Sky Sports pundits working on the game reacted with incredulity.

Gary Neville, the former Manchester and England full-back, said: "I've never seen an official raise an elbow to a player. I think he'll be in a lot of trouble after this game ends."

Ex-Manchester City and England defender Micah Richards added: "I've never seen anything like that in my life."

Former Manchester United captain Roy Keane focused on Robertson's role in the incident, calling the Scot "a big baby".

"He should be more worried about his defending," said Keane. "Do you know what he is, that Robertson? I've watched him a number of times, he is a big baby, that's what that guy is.

"Just get on with the game and concentrate on your defending. He does grab the linesman first."