The Professional Game Match Officials Limited (PGMOL), the body responsible for match officials across English football, is to investigate an alleged elbow by assistant referee Constantine Hatzidakis on Liverpool defender Andrew Robertson during Sunday's Premier League game against Arsenal.
As the teams left the pitch for the half-time whistle, Robertson approached Hatzidakis and grabbed his arm. Television replays appeared to suggest the assistant raised his elbow and caught Robertson in the face.
The Scotland international was incensed, and was booked by referee Paul Tierney in the aftermath.
A statement read: "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."
No action was taken at half-time and the assistant continued to run the line in the second half.
Liverpool came back from two goals down to claim a dramatic 2-2 draw against Arsenal.