The Imps have given the Grantham striker the chance to win a himself a league contract after he impressed during a spell in the reserves. He has now joined the club for pre-season training which will allow Jacko to run his expert eye over the striker.
Assistant boss Iffy Onuora is impressed with the 19 goal forwards performance so far.
"We've taken Sam on trial because, on the few occasions he played for the reserves, he impressed. We invited him back for the manager to have a good look at him and so far he's not looked out of place at all."
Iffy outlined the attributes Mullarkey will bring to the side.
"Physically he's in very good shape, he's strong, quick, he may be a little quiet but that's to be expected. But he's a toughie and I just think the manager now wants to see him in a competitive environment in terms of games. Once we've seen that, we'll take it from there."
Mullarkey joins the Imps as they hunt for a striker to complete Jacko's 'Magnificent Seven'. City are still in the hunt for Michael Boulding, and rumours are abound that they may have had discussions with Luke Beckett, but as yet the striker hunt has appeared to be elusive for Jacko.