Liverpool were fuming as defender Andy Robertson appeared to be elbowed by an assistant referee at the end of the first half of Sunday's game against Arsenal.

The left-back approached the official, who was identified by Sky Sports as Constantine Hatzidakis, and seemed to be making a point to him.

It was unclear from a distance what was said, but television pictures then looked to show the assistant referee raise his right elbow and make contact with the Scotland international.

What was not obvious was whether the linesman had intended to catch Robertson.

Asked if he had ever seen anything like it, pundit and former Manchester United hard man Roy Keane said: "No, not really, but Robertson, does he grab the linesman first? I'm not sure, but Robertson then is complaining.

"He should be more worried about his defending."

Keane then pointed the finger at Robertson and described him as "a big baby".

"You know what he is, that Robertson," Keane said. "I've watched him a number of times, he is a big baby. Just get on with the game and concentrate on your defending. He does grab the linesman first."

According to Sky Sports, Robertson said on entering the tunnel at half-time: "The linesman has elbowed me in the throat."

Liverpool captain Jordan Henderson reportedly complained to referee Paul Tierney, before the players entered the dressing room.