Radio host Alan Brazil has revealed he was sent a death threat in the post by someone claiming to be from the Green Brigade.
The 60-year-old, who began his career as a youth with Celtic Boys Club, dropped the bombshell during his radio show, the Alan Brazil Sports Breakfast on the talkSPORT station.
Speaking to fellow pundit and former Rangers striker and manager Ally McCoist, Brazil said he had been sent a picture of a gun, with the message: "The next time you come to Glasgow, you're getting it."
The former Manchester United striker did not contact police at the time, but admitted he was mystified as to what had prompted the chilling message.
He said: "I didn't take any action with it, but a while ago someone so-called from the Green Brigade sent a picture of a gun to me saying, 'Next time you come to Glasgow you're getting it'.
"Can you believe that? I'm serious - I don't even know what I said."
Fans blast 'vindictive' club
The fans group are currently at loggerheads with the Hoops hierarchy, claiming that the club is blocking ticket sales for members who sit in that area of the Celtic Park stadium.
A strongly-worded statement published yesterday branded the club "vindictive", with the supporters group revealing that they face missing out on the Betfred Cup final and Old Firm clash at the end of December because of the decision to withhold briefs from members.
Celtic announced a partial closure of the Green Brigade section for tomorrow night's Europa League match against Rennes amid ongoing safety concerns. The champions have been hit with more than £34,000 in fines from UEFA as a result of fan conduct at European games.
In the statement, the group said: 'We know the use of pyrotechnics may bring consequences and therefore accept the inevitable sanctions.
"We regret that any fans outside of our membership should suffer those consequences and point to that being disproportionate and unnecessary.
"Considering we met with the club last week to discuss potential sanctions, the timing and scope of this decision is particularly vindictive."
'Good on them' - McCoist backs Hoops
McCoist is backing the Celtic board as they attempt to clamp down on the group, branding some of the supporters "a complete embarrassment".
He added: "Celtic don't need it. The amount of times they have been fined is absolutely ridiculous. [The Green Brigade] creates a good atmosphere but I think there's a section of them who have been a complete and utter embarrassment [to Celtic].
"Celtic will be sick of it and they are trying to do something about it, good on them."