Riefenhauser was optioned to Triple-A Iowa on Friday.
Riefenhauser will head down to minor league camp after a rough start to spring training in which he allowed two home runs and three earned runs over just 3.2 innings of work. There was some belief that the release of Rex Brothers would help Riefenhauser's chances at making the Opening Day roster, but his struggles on the mound ultimately snuffed out that opportunity. He'll start the year in the bullpen at Triple-A Iowa in all likelihood.