Niese, 27, was hit in the side by a line drive during his last start and was removed from the game, but that is not why he is heading to the DL. He missed time with a sore shoulder in spring training and spent close to two months on the shelf with shoulder inflammation and a partially torn rotator cuff last summer.
It's worth noting Niese's velocity has fallen off a bit in recent starts, which is a classic symptom of shoulder problems. From the indispensable Brooks Baseball:
In 17 starts and 103 1/3 innings this season, Niese has gone 5-4 with a 2.96 ERA (118 ERA+). He is owed approximately $18.5 million through 2016 with club options for both 2017 and 2018, so he has been constantly mentioned as a trade chip. Jon Heyman recently reported the team is hesitant to trade him, however. The shoulder injury figures to bring any trade chatter to a halt.
Right-hander Buddy Carlyle, 36, was called up to take Niese's spot on the roster. He threw 4 1/3 scoreless innings for New York earlier this season after not pitching in MLB since 2011. The team has not yet announced who will replace Niese in the rotation.