The flag was seen in the section housing the away support during the Celtic v Hibernian Scottish Premiership match on December 7.
A number of days after the match the Orange Order made a complaint to the Police about the banner.
The flag was a green, white and orange tricolour flag with a Heart of Midlothian logo in the centre with the words ‘We’ll never be mastered by no orange b****** printed on it’.
The Orange Order said they made complaints to the Police Scotland, the SPFL, Celtic and Hibernian over the banner.
Police said it was being investigated as a hate crime.
A previous banner was displayed in the home end at a Hibernian v Rangers match at Easter Road showing a figure in an orange sash and bowler hat with a diagonal red line through it.
A spokesperson for the Orange Order said: “We wrote to the CEO of Hibernian FC, CEO of Celtic FC, Neil Doncaster SPFL, and Police Scotland, regarding the hate banner that was displayed at Celtic Park last weekend within the away support.
“This is the 2nd time this has happened this year within the Hibs support, displaying hate banners against our Institution.
“Hibs did write back to us earlier this year saying they would not allow any such banner to be displayed again at Easter Road which we thanked them for.
“We have had a response from Police Scotland saying they are looking into our complaint.”
A Police Scotland spokesperson said: “Following the Celtic vs Hibernian match on Sunday, December 7, 2024 at Celtic Park, we received a report of an offensive flag having been flown in the away section.
“This matter was not reported to police or stewards during the fixture. Enquiries are ongoing and it is being investigated as a hate crime.”
