Refereeing body PGMOL will investigate after Liverpool's Andy Robertson appeared to be elbowed in the chin by assistant referee Constantine Hatzidakis.

Robertson approached the official angrily at the end of the first half against Arsenal and appeared to shove him as he passed, with Hatzidakis raising an elbow which hit Robertson.

The Scot reacted furiously and, along with several team-mates, approached referee Paul Tierney, who booked 29-year-old Robertson.

The Anfield game ended 2-2 with Liverpool coming from 2-0 down to draw with the league leaders.

Former Premier League striker Chris Sutton was watching the game for BBC Radio 5 Live and thinks Hatzidakis should be punished.

"I really don't know what he was thinking. As far as I can see, he has to be banned," said Sutton."He will have to sit out a number of games. I can't remember another incident like this. Where is the precedent for these things?"

Sky Sports pundit Roy Keane called the Reds player a "big baby" for his reaction.

"Robertson should be more worried about his defending," said Keane. "Just get on with the game. He grabs the linesman first."

Robertson could be in trouble if the incident is investigated further. Fulham's Aleksandar Mitrovic is currently serving an eight-game ban for pushing referee Chris Kavanagh in their FA Cup loss at Manchester United on 19 March.

Sutton added: "A big debating point was Mitrovic and the eight-game ban and the FA want him banned for more but you can't have assistants throwing elbows. What should the punishment be?"

PGMOL's statement said it was "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", adding that it would "review the matter in full".