SECTARIANISM unfurled an ugly face after the Old Firm clash on Tuesday night when prowlers planted a Union flag in the garden of Martin O'Neill, the Celtic manager.

The 6ft by 4ft flag ''was driven into the ground as if it was a moon landing'', a source close to Mr O'Neill told The Herald. Union flags are traditionally waved by Rangers supporters.

Rangers won the CIS Insurance Cup semi-final 2-1 in extra time after Bert Konterman wrecked Celtic's dream of a second successive domestic treble.

A ''frightened'' Geraldine O'Neill called police to the couple's home in Kelvinside after the incident, at about 11.30pm. Mrs O'Neill was at home with one of the couple's daughters.

The Celtic source added: ''There is something insidious about the whole thing. The O'Neill family should be able to go about their lives in privacy.''

A spokeswoman for Strathclyde Police said: ''We attended at a house in Glasgow and removed a flag from the front garden. Inquiries are continuing into the incident.''

A Celtic spokeswoman said: ''It is deeply regrettable that such an incident has occurred as it has obviously caused some distress to Martin O'Neill's family.''

A spokesman for the Affiliation of Celtic Supporters' Clubs declined to comment other than to say: ''We'll take a raincheck on that one.''