Police Scotland are investigating the abusive and threatening messages sent to referee Kevin Clancy following Saturday's Old Firm.
The messages, which were condemned by the Scottish Football Association (SFA) and Rangers, were referred to Police Scotland after the personal and professional contact details of Clancy, who took charge at Celtic Park, were published online after the match.
A Police Scotland spokesperson said: "We are investigating alleged threatening communications which were reported to us by the SFA today (Tuesday, 11 April).
"All reports of this nature are treated with the utmost seriousness and will be investigated thoroughly.
"We will provide support to those affected as our investigation progresses."
