Stephenson, the No. 2 prospect, was optioned to Triple-A Louisville along with pitcher Stephen Johnson and outfielder Kyle Waldrop.
Pitchers Zack Weiss and Tim Adleman and catcher Joe Hudson were reassigned to the Minor League camp.
Left-handed pitcher Jonathan Sanchez, signed as a free agent to a Minor League deal shortly before Spring Training, was released. Sanchez was trying to come back after not pitching in the Majors since 2013.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, follow him on Twitter @m_sheldon and Facebook and listen to his podcast.