McNabb, 23, has played in 37 games for the Buffalo Sabres, with one goal, seven assists and 21 penalty minutes. He was acquired by the Kings on March 5 in a trade for forward/defenseman Nicolas Deslauriers and right wing Hudson Fasching.
McNabb played 52 games in the American Hockey League last season, for the Manchester Monarchs and Rochester Americans; he had 36 points (10 goals), 63 penalty minutes, and a plus-14 rating.
McNabb was selected by the Sabres in the third round (No. 66) of the 2009 NHL Draft.
Andreoff, 23, played 76 games last season for Manchester; he had 35 points (11 goals), 133 penalty minutes and a plus-5 rating. He was selected by the Kings in the third round (No. 80) of the 2011 draft.