Nelson is expected to compete with Tommy Henry for the final spot in the rotation, Steve Gilbert of MLB.com reports.
The top three in the rotation are set -- Zac Gallen, Merrill Kelly, Eduardo Rodriguez -- and it looks like Brandon Pfaadt has the edge for the No. 4 spot, leaving Nelson and Henry to compete for the back end. Nelson spent the first four-and-a-half months of the 2023 season as part of the rotation before an August demotion. He returned to the Diamondbacks in September and made three postseason appearances as a reliever. Nelson recorded an 8-8 record and 5.31 ERA over 144 innings (29 appearances, 27 starts) with 96 strikeouts and 46 walks during the regular season.