Nelson has been shut down from throwing after experiencing lower-body discomfort coming out of Wednesday's bullpen session, Ken Gurnick of MLB.com reports.
Nelson's latest health-related setback is presumably related to the groin and lower-back injuries that had hampered him earlier in camp. Though Opening Day is still about a month away, Nelson's shutdown likely means that even if he's cleared to resume a throwing program next week, he won't have enough time to get the innings he needs this spring to stake his claim to a rotation or bullpen spot.