Hundreds of fake merchandise like hats, placards, scarves and flags were seized.
The discoveries took place in the Dublin 4 area near the Aviva Stadium during the Manchester Utd v Sampdoria friendly.
17 out of 21 vendors inspected in the area were found to be selling counterfeit goods.
Gardaí, Customs officers and Dublin City Council officials were involved in the operation, alongside representatives from Man Utd and Adidas.
In total, around 225 hats, 200 placards, 140 flags and 2,220 scarves worth around €25,000 were seized.