The forward has joined St Johnstone on loan until the end of the campaign, having struggled to hold down a starting slot at Tannadice.
He had been competing against summer signing Mario Bilate to partner Nadir Ciftci in attack and was uncertain that he would feature regularly as a result. "Brian has been a bit limited in terms of appearances this season as well as last year and he is a bit frustrated about that," said McNamara, who is also trying to offload midfielder Michael Gardyne.
"I see the two other strikers ahead of him. At this stage of Brian's career, he wants to try to get regular football which I couldn't guarantee."