Liverpool left-back Andy Robertson was struck on the face by assistant referee Constantine Hatzidakis in a remarkable incident just after the half-time whistle of Sunday's Premier League clash with Arsenal.

The Scotland captain approached the linesman, who then thrust his elbow into Robertson's chin.

Robertson was then shown a yellow card by referee Paul Tierney as he furiously protested.

Arsenal led 2-1 at half-time, but Liverpool rescued a 2-2 draw as Roberto Firmino's 87th-minute header dented the leaders' bid to win the title for the first time since 2004.

Hatzidakis now faces an investigation into his conduct after referees' governing body PGMOL said they would review the incident.

"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," the statement said.

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

Former Manchester United midfielder Roy Keane, working at Anfield as a Sky Sports pundit, was unimpressed with Robertson's reaction to the clash.

"Does Robertson grab the linesman first? I'm not sure but Robertson's then complaining," Keane said.

"He should be more worried about his defending. 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."

Fulham striker Aleksandar Mitrovic was this week given an eight-match ban for pushing referee Chris Kavanagh in the Cottagers' FA Cup defeat against Manchester United last month.

But former Manchester United defender Gary Neville believes it will be Hatzidakis who finds himself in trouble this time.

"I've never seen an official raise an elbow to a player," Neville said on Sky Sports. "I think he'll be in a lot of trouble after this game ends."