Arthur Staple of Newsday reported the nature of the injury, according to a source, Tuesday after the Islanders' 6-4 win in Game 4 of their Eastern Conference Quarterfinal series with the Pittsburgh Penguins. The best-of-7 series is tied 2-2, with Game 5 set for Thursday at Consol Energy Center in Pittsburgh (7 p.m. ET, NBCSN, TSN).
MacDonald headed to the dressing room with about seven minutes remaining in the second period of Game 4, and Islanders coach Jack Capuano called it an upper-body injury.
MacDonald, a top-four blueliner for New York, was on the receiving end of a slap shot by Pittsburgh Penguins defenseman Douglas Murray. MacDonald also was given a holding penalty during the sequence -- Keith Aucoin served the two minutes -- and he did not return to the game.