The linesman who chalked off a goal in the crunch Old Firm game has received knife threats from Celtic fans.
Police yesterday warned match official Gordon McBride to watch out for his safety after a terror letter was sent to the Daily Record.
A group calling themselves Johnstone Celtic Bhoys threatened to "make an example" of Mr McBride.
They described said he would be slashed with a knife or attacked with baseball bats.
The Record immediately passed the letter to police.
Mr McBride was at the centre of controversy last week when he flagged to disallow a Celtic goal.
It would have tied the match at 2-2, but Rangers went on to win 3-1.
Later, we revealed that Mr McBride had worn a Rangers strip at a charity match and was on an Ibrox mailing list.
The thugs' threatening letter said: "We now intend to make an example of Mr McBride.
"Whether this means McBride's face cut open with a knife or set about with baseball bats, then so be it.
"He is in danger of a very serious attack. McBride will not escape punishment."
Last night, Celtic distanced themselves from the thugs and manager Tommy Burns described the letter as "deplorable".
He said: "Whoever sent that letter should be ashamed. People like that are not welcome as part of Celtic or Scottish football."
Celtic Supporters' Association president Frank Hinton said: "People who react like this are nutcases.
"They are not doing Celtic or themselves any favours.
"I know how upset the fans were and that they were even more upset to find out he's a Rangers supporter.
"But to react like this is ridiculous."
John Martin Costigane, secretary of Johnstone Celtic Supporters' Club, said the letter had nothing to do with his members.
And he added: "I find its contents deplorable."
Police visited Mr McBride yesterday to warn him about the threats.
And forensic experts will now examine the letter for fingerprints in a bid to track down the culprits.
Mr McBride wasn't available for comment last night.