"Just said he didn't feel that great after the outing, so we sent him back to Phoenix to be evaluated," D-backs manager Chip Hale said.
Hale was asked whether it was Bradley's elbow or shoulder that was giving him issues and he said he did not have that information yet, but that more could come following Thursday afternoon's game against the Rockies.
Bradley, who has been on the disabled list with what the club said was tendinitis in his shoulder, allowed three runs on six hits while striking out three over four innings on Wednesday night.
"He threw OK," Hale said.
Bradley had been scheduled to make another rehab start for Reno before the team decided whether or not to activate him.