The Diamondbacks placed Nelson on the 15-day injured list Friday with a strained right elbow.
John Gambadoro of Arizona Sports 98.7 FM says it's a partially torn flexor tendon for Nelson, who held the Angels to two runs over seven innings in his last start Monday. There's been no timetable provided by the Diamondbacks yet, but the nature of the injury points to the likelihood of a lengthy absence for Nelson. Brandon Pfaadt is a candidate to replace Nelson in the Arizona rotation.