Nelson (elbow) struck out two over a scoreless inning for Single-A Visalia on Saturday.
Nelson began a rehab assignment with the Rawhide and set down the side in order in the first inning. Although he opened the season as a starter for the Diamondbacks, the club plans to have him pitch out of the bullpen over the final month of the regular season. MLB.com targets the right-hander's possible return for Friday, when the Diamondbacks begin a homestand against the Rangers.