A 59-year-old man is being questioned by officers at a police station, after a still image emerged from the fourth round clash at Anfield on Saturday afternoon
Match Commander, Chief Superintendent Jon Ward, had earlier confirmed footage of the game was being reviewed following the emergence of a still image on Twitter.
A 59-year-old man has now been taken to a police station and is undergoing questioning by officers.
A statement read: "Merseyside Police can confirm that a 59-year-old man from North Wales, has been arrested this evening following an alleged incident at the LFC vs MUFC match this afternoon. (Saturday, 28 January).
"The man has been taken to a police station, and will be questioned by officers.
"Merseyside Police would like to thank North Wales police and Liverpool Football Club for their assistance with this matter."
The game was expected to be highly charged following an incident involving Luis Suarez and Patrice Evra earlier this season, which saw the Uruguayan banned for eight games for alleged racist abuse of the defender.
Liverpool defeated Sir Alex Ferguson's side 2-1 in the fourth round clash at Anfield on Saturday afternoon, thanks to goals from Daniel Agger and Dirk Kuyt either side of Park Ji Sung's equaliser.