Nelson was placed on the 15-day injured list Thursday with left elbow inflammation.
The 26-year-old apparently suffered the injury Monday against the Dodgers, when he allowed three runs on a hit and a walk without recording an out. It's been a breakout campaign for Nelson with a 2.19 ERA, 1.08 WHIP and 30:14 K:BB over 37 innings this year, but the elbow injury could bring his season to an early end.