The 20-year-old spent four days training with the Dons this week after being sent north by Anfield manager Kenny Dalglish.
The youngster impressed but he is not what Brown is looking for as he bids to bolster his squad for the remainder of the SPL season.
The manager told the Press & Journal: "Irwin is a good player and, although he might be back up at some stage, he is not one we will be taking on just now. He did well and Kenny Dalglish speaks highly of him but he duplicates what we have already. We need a different kind of midfield player."